JPS61250993A - El element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Technical Field of the Invention) The present invention relates to a KL (KL) used as a light emitting display device or a surface light source.
The invention relates to electroluminescent (electroluminescent) elements.

(Prior art and its problems) A fluorescent material that emits light by applying a voltage to it.
Since the discovery of so-called electroluminescence, much research and development has been conducted with the aim of applying it to surface light sources and display devices. Various configurations of EL elements have been proposed and studied, but AC-driven thin-film EL elements, in which a thin-film EL light-emitting layer is sandwiched between insulating thin films from both sides, have excellent light-emitting characteristics and stability, and are the most suitable for information terminals. It is put into practical use as a display, etc. FIG. 3 shows the basic structure of this typical double-insulated thin film EL device. (Niss, I.D. 74 Digest Op Technical Papers, p. 84,
5ID74 digest of technica
l papers).

A transparent electrode such as ITO or Nesa film 32° thin film first anti-green body layer 33 on the glass substrate 3, Zn8: Mn + Zn
8: 'rbi'.

Light emitting layer 34, such as a thin film. Furthermore, a thin second permanent green body layer 3 is formed thereon.
5. It has a multilayer thin film structure consisting of a back electrode 36 such as an AJ thin film. The first and second green body layers are Y, 0. .

Ta20H, A7205y8i3N4, BaTi
It is a transparent dielectric thin film of O3, 5rTi03, etc. with a thickness of about 0.2 μm to 1 μm, and is formed by cis battering, vacuum evaporation, or the like. This thin film insulating layer prevents excessive current from flowing within the light emitting layer due to the application of high voltage, preventing destruction, and protecting the light emitting layer from moisture and harmful ion contamination, improving reliability. It also plays a role in improving the luminance and luminous efficiency of the device.

However, even in such an element configuration, there are many practical problems. In other words, in applications such as display devices and surface light sources, it is extremely difficult to completely eliminate defects that can cause dielectric breakdown of the device over a fairly wide area, and manufacturing steps are required because the initial voltage application causes device breakdown. The reason is that the running distance is low. In addition, the drive voltage required to cause the device to emit light must be high because it is applied to the non-green material layer in parts, and the drive circuit also has the disadvantage of being expensive.

In order to reduce the drawbacks of these conventional thin-film EL devices, studies have been conducted on EL devices that employ a high dielectric constant ceramic layer made from fired powder raw materials instead of the thin-film non-green material layer. An example of this type II device is shown in FIG. On the substrate 41, an electrode 42, a high dielectric constant ceramic material layer 43,
Thin film light emitting layer 44, thin film second evergreen layer 45, transparent electrode 46
It has a basic structure consisting of. Incidentally, the thin film second evergreen body layer 45 does not necessarily have to be provided. An EL element having such a structure can be manufactured by using laminated ceramic technology or a combination of thick film technology and thin film technology. Here, by using a high dielectric constant ceramic or a composite perovskite material containing BaTi0j or PB as the dielectric layer, a dielectric constant of from 1,000 to 20,000 or more can be realized. Therefore, even if the thickness of the ceramic ceramic layer is 10 .mu.m or more, the ceramic layer can have a large capacity equivalent to or higher than that obtained when a conventional thin film layer is used. In addition, with such a thick layer, the dielectric strength voltage is extremely high (and even in the case of an EL element, there will be no breakdown of the element due to dielectric breakdown at a practical applied voltage. Since the capacitance is large, the capacitance division of the driving voltage is reduced and the voltage is effectively applied to the effective layer, so that the driving voltage can be lowered.

As described above, by employing a high dielectric constant ceramic layer as a non-green material layer of an EL element, a significant improvement in yield and driving voltage can be realized. However, when such an element is allowed to emit light for a long time, the luminance decreases, which poses a practical problem.

(Objective of the Invention) As described above, the object of the present invention is to provide an EL element that prevents a decrease in brightness without impairing the advantages of an EL element in which a high dielectric constant ceramic layer is used as an antigreen layer.

(Structure of the Invention and Detailed Description thereof) According to the present invention, there is provided an EL element in which a light-emitting layer and a high-permittivity ceramic insulating layer are sandwiched between two electrodes, or a high-permittivity ceramic layer is sandwiched between two electrodes. In an EL device in which a green insulator layer, a light emitting layer, and a thin film insulator layer are laminated and sandwiched, a thin film insulator layer is interposed between the high dielectric constant ceramic insulator layer and the light emitting layer. An EL element characterized by this can be obtained.

The basic structure of the KL element of the present invention is shown in FIG.

An electrode 12 on a substrate 11 and a high dielectric constant ceramic material layer 1
3. It is composed of a thin film insulator intervening layer 17, a light emitting layer 14, a thin film second evergreen layer 15, and a transparent electrode 16. In short, a thin film insulator intervening layer is inserted into the EL element structure using the high dielectric constant ceramic layer shown in FIG. In addition,
The present invention is characterized by providing an intervening layer between the high dielectric constant ceramic layer and the light emitting layer, and the other constituent parts of the EL element need not be as shown in FIG. 1.

For example, thin! A so-called single insulation structure may be used, in which the second insulating layer 15 is eliminated, or a structure in which the high dielectric constant ceramic layer is made thicker and the substrate 11 is eliminated. In addition, the thin film insulator intervening layer is an insulator thin film formed by sputtering, air vapor deposition, plasma CVD, etc., and does not necessarily have to be transparent, but may be a thin film that is colored to improve contrast. But that's fine. Generally Ta105,
Y2O3,8i02.

8i0, SmzOB, Al2O3, BaTiO
Stable oxides such as 315rTi03, insulating nitrides such as 8i3N4, fluorides such as CaF1, etc. can be used. Also, it is not necessary to increase the thickness of this intervening layer (approximately 0.02 to 0.2 μm). Also, if it is made very thin, it will not be possible to sufficiently prevent the brightness of the EL element from decreasing.Furthermore, an EL element that uses a high dielectric constant ceramic layer as an anti-green layer will decrease its brightness after long-term use. Although the cause of this is unknown, it is thought to be due to the diffusion of harmful ions from the ceramic layer to the luminescent layer and the interface with the luminescent layer.

It is believed that the adoption of the thin film insulator intervening layer of the present invention prevents the diffusion of these harmful ions. Moreover, when the thickness of the intervening layer is particularly set to about 0.1 μm or less, there is almost no need to increase the driving voltage even if the intervening layer is inserted, and in some cases, the brightness is slightly improved.

(Example) A 13L element having the cross-sectional structure shown in FIG. 1 was prepared. Each manufacturing process is as follows.

A powder made of alumina and lead borosilicate glass was mixed with a binder to form a slurry, and then cast to form a film to create a green sheet with a thickness of 0.7 M that would serve as a ceramic substrate. On this ceramic green sheet, an Ag-Pd paste consisting of 85 atomic percent Ag and 15 atomic percent Pb was formed into a striped pattern with a width of 0.55 mm and a pitch of 1.1 mm. It was set as electrode 12.

Pb (Fet7s w, 7.) as a Pb-containing composite perovskite material for low humidity firing. R(Fe1/2
A green sheet for the dielectric ceramic constant green material layer 13 having a thickness of 40 μm was prepared by mixing a binder with a pre-fired powder of Nb, /, ) oyos and casting a film. This green sheet was laminated and crimped onto the substrate green sheet on which the 12 electrode patterns described above were printed, the unnecessary portions at the ends were cut off, and then fired at 950° C. to produce a laminated ceramic structure. This firing caused about 10% shrinkage, but no warping occurred.

Next, a Ta20B film was formed to a thickness of 0.05 μm by high frequency magnetron sputtering to form a thin film insulator intervening layer 17.

Next, by the co-evaporation method of Zn8 and Mn,! l) ZnS:
Mn was vacuum deposited to a thickness of 10.3 μm. In order to improve the characteristics, heat treatment was performed at 550° C. for 2 hours in Ar. Thereafter, a Taxes thin film was formed again to a thickness of 0.3 μm by high-frequency magnetron sputtering to form a thin second permanent green body layer 15. Furthermore, fi, ITO was deposited by sputtering method.
A film was formed to a thickness of 0.3 μm by high frequency magnetron sputtering. At this time, the ITO film was patterned in advance with a resist so as to be orthogonal to the λg-Pd thick film stripe electrode, and the ITO film was formed into a stripe shape using a lift-off method to form the transparent electrode 16.

When an AC pulse voltage was applied to the EL element created in this way, it started emitting light at 50V, then at 80V and 200V.
High brightness was obtained at a low voltage of about 200 cd/- at Hz. The ceramic layer was dark brown, allowing for a high-contrast luminescent display. Further, even when an excessive voltage of 150 V was applied, there was no element breakdown due to dielectric breakdown.

This element was heated at 200 Hz, 80 Hz in a dry nitrogen atmosphere.
Figure 2 shows the change in brightness when emitting light at V for a long time. Almost no decrease in brightness was observed even after 1000 hours of lighting. For comparison, FIG. 2 also shows the results of a long-time lighting test of a conventional EL element without a thin film insulator intervening layer. Test conditions are the same.

This element exhibited a considerable decrease in brightness after approximately 100 hours of driving, and showed a tendency for the brightness to continue to decrease gradually thereafter. As described above, the reduction in brightness has been significantly reduced by employing the thin film insulator intervening layer. The effect of such an intervening layer is Ta
In addition to 105, there are AJ, O,, Y, 0. .

8iN etc. were almost the same. Also Zn8: Mn
In addition, insulated light emitting Zn8: TbF3 and red light emitting Z
n8: Even when SmF3 or the like is used as the light emitting layer, the effect of the thin film insulator intervening layer is the same, demonstrating the effectiveness of the KL element structure of the present invention.

(Effects of the Invention) As explained above, the EL element of the present invention is driven at low voltage, emits light with high brightness, has high contrast, and employs a high-permittivity ceramic non-green material layer that does not cause element breakdown due to dielectric breakdown and has high walkthrough. This provides long-term stabilization of brightness characteristics without sacrificing the advantages of the KL element, which has great industrial value.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional structural diagram of the EL element of the present invention. FIG. 2 shows changes over time in the luminance characteristics of the EL device of this embodiment and the conventional product. FIG. 3 is a cross-sectional structural diagram of a double-insulated thin film EL element, which is a general L element, and FIG. 4 is a cross-sectional structural diagram of an EL element employing a high dielectric constant ceramic non-green material layer. 11.41... Substrate, 12.42... Electrode, 13.
43... High dielectric constant ceramic permanent green layer, 14,34.
44...Light emitting layer, 15,35.45...Thin film second evergreen layer, 16.32.46...Transparent electrode, 17...
Thin film insulator intervening layer, 31... glass substrate, 33...
Thin film first evergreen body layer, 36... back electrode. O 1 Figure O 2 Figure + 10 10210310' Time 71-3 Figure OI

Claims (1)

[Claims] An EL element in which an EL light emitting layer and a high dielectric constant ceramic insulator layer are sandwiched between two electrodes, or a high dielectric constant ceramic insulator layer, an EL light emitting layer, and a thin film insulator layer are stacked and sandwiched between two electrodes. An EL device characterized in that a thin insulating layer is interposed between the high dielectric constant ceramic constant green layer and the EL light emitting layer.