JPS6338982A - Electroluminescence element - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electroluminescent element used as a display of a computer terminal or the like.

BACKGROUND OF THE INVENTION Electroluminescent (EL) elements utilize the phenomenon of emitting light when an electric field is applied to a semiconductor such as a phosphor, and are used as display elements. E
The L element is formed from a light-emitting layer and a pair of electrodes that apply an electric field to the light-emitting layer.Thin-film EL elements with an insulating structure in which an insulating layer is provided between the light-emitting layer and one or both electrodes have high reliability. It is widely used because of its high

However, the EL element with this structure has a problem in that the required driving voltage is high (for example, 200 V or more) because the applied voltage is divided between the absolute RM and the light emitting layer.

In order to improve this, attempts have been made to use a ferroelectric material in the insulating layer (Kuwata et al., Institute of Electronics and Communication Engineers, Technical Research Report ED85-6). As a result, 5rTiOa and P b
It has been found that it is effective to use a perovskite-type ferroelectric material with a high dielectric constant, such as T i O. However, these ferroelectric materials have propagation type (non-self-healing type) dielectric breakdown characteristics with respect to aluminum electrodes, and therefore do not function satisfactorily as an insulating layer.

In order to solve this problem, it has also been proposed to use a self-healing dielectric with a small dielectric constant between the light emitting layer and the AQ electrode. (Japanese Unexamined Patent Publication No. 60-25199).

An object of the present invention is to provide an EL probe that can be driven at low voltage and has high reliability.

Structure of the Invention The EL device of the present invention includes a light-emitting layer that emits light when an electric field is applied, a back electrode and a transparent electrode that apply an electric field to the light-emitting layer, and an insulating layer between at least the light-emitting layer and the back electrode. The electroluminescent device provided with a layer is characterized in that a thin layer exhibiting non-ohmic electrical conduction is provided between the insulating layer and the back electrode.

Hereinafter, the present invention will be described in further detail with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an example of the configuration of an EL element. A transparent electrode 13 is provided on a transparent substrate 11, and a light emitting layer 17 is further provided thereon with a first insulating layer 15 interposed therebetween. A second insulating layer 19 and a non-ohmic electrically conductive layer 21 are sequentially laminated on this light emitting layer 17, and a back electrode 23 is further formed thereon to constitute a thin film type EL element.

The non-ohmic electrically conductive layer 21 exhibits non-ohmic electrical conduction. This layer 21 is made of, for example, a layer containing ZnO as a main component, preferably Co, Bi, La, Mg, Pr.
, doped with impurities such as Sb, Mn, and Cr6
The concentration of each doping substance is 0.05-5mol%
degree is suitable.

The thickness of the second non-ohmic electrically conductive layer is preferably about 001 to 10 μm.

The main feature of the present invention is to provide a non-ohmic electrically conductive layer between the insulating layer and the back electrode, and other configurations and materials are not particularly limited, and conventionally known materials can be used. can.

In particular, as a material for the insulating layer, Ca T I O3,5r
It becomes possible to use perovskite-type strong derivatives such as Ti03 and P b T i O.

Although such a ferroelectric material can greatly reduce the driving voltage, since it causes propagation type dielectric breakdown, conventionally, a solid layer has been preferably used. In contrast, in the present invention, by providing a non-ohmic electrically conductive layer, the dielectric breakdown becomes self-healing, making it easy to use the above-mentioned ferroelectric material. As the insulating layer material, a dielectric material containing Ti is particularly preferable. In addition, examples of materials for the absolute a-layer other than those mentioned above include Tie, BaTiO3, and the like.

The thickness of the first and second insulating layers 15.19 is between 0.1 and 15.19.
Approximately 1.0 μm is suitable.

As the transparent substrate 11, glass, plastic, etc. are used.

As the transparent electrode 13, ITO (Indium-T
In-Oxide), tin oxide, indium oxide, etc. are used. In the EL element, either one of the two electrodes (transparent electrode 13, back electrode 23) provided in the light emitting layer may be transparent or opaque.

The light emitting layer 19 is made of ZnS:Pb, Cu, CQ, ZnS:C
u, AQ, ZnS: Mn, Cu, Zn(S.

Ss): Cu, 1. ZnS: Cu, SrS: Ce, Ba
, ZnS:Mn, CaS:Ce, ZnS:Te.

Mn, CaS:Eu, etc. are used.

The back electrode 23 is made of a metal material such as aluminum or the above-mentioned transparent electrode material.

Each layer and electrode in the EL element can be formed by a thin film forming method such as vacuum evaporation, sputtering, or ion blasting.

According to the present invention, by providing a non-ohmic electrically conductive layer between the insulating layer and the back electrode in the EL element, expansion of the dielectric breakdown area is prevented and the ferroelectric insulation between the light emitting layer and the ferroelectric insulation layer is prevented. This enables stable light emission with a relatively low driving voltage, resulting in a high-luminance, low-voltage driving, and highly reliable EL element.

Example 1 An ITO transparent electrode is formed as a thin film of 1,000 layers on a glass substrate by sputtering. On top of that, CaTi0. 2 insulation layers
It was formed to a thickness of 1,000 people.

Raw material: 4N CaTi0:+ fired product substrate temperature =
400°C Reaction pressure 2 x 1O-4 Torr atmosphere Air: Oxygen RF power = 50W Acceleration voltage knee 5oov On this insulating layer, a 1 μm thick SrS:Ce light emitting layer was formed at a substrate temperature of 450°C by electron beam evaporation. Formed.

On this light emitting layer, Ca T x
An O3 insulating layer was formed.

Furthermore, on this insulating layer, a ZnO layer (non-ohmic electrically conductive layer) with a thickness of 1 μm is formed by sputtering under the following conditions.
was formed.

Target: Co　O, B　i, o, on ZnO.

La20. 0.5 mo1% of each was added and fired in a sputtering pressure crab atmosphere of 1.5 x 10-2 Torr.
Air: Mixed gas of oxygen and argon Substrate temperature = 300°C Deposition rate: 1 μm/hour RF power: 200
Figure 2 shows the current-voltage characteristics of m).

It can be seen that this film exhibits non-ohmic electrical conduction.

Next, on this ZnO layer, an AQ group electrode was formed to a film thickness of 500 mm by sputtering to produce an EL element.

When an AC pulse voltage of 5K)+Z was applied to this ELi element and the EL characteristics were investigated, it was found that the luminance was approximately saturated at a driving voltage of about 90V and stable light emission was achieved as shown in FIG. Further, when the voltage was increased by one more, dielectric breakdown occurred, but it was a self-recovery type and did not spread.

Example 2 After forming an ITO transparent electrode on a glass substrate in the same manner as in Example 1, an insulating layer of 5rTiO was formed to a thickness of 2,000 yen by ion blasting under the following conditions.

Raw material: 4N 5rTiO, fired product Substrate temperature: 4
00°C Reaction pressure 2 x 10-'Torr atmosphere Air: Oxygen RF power: 501i1 Acceleration voltage knee 300V On this insulating layer, a 1 μm thick CaS:Ce light-emitting layer was formed at a substrate temperature of 400°C by electron beam evaporation. Formed.

On this light emitting layer, S r T x is applied again in the same manner as above.
An O3 insulating layer was formed.

Furthermore, on this insulating layer, a ZnO layer (non-ohmic electrically conductive layer) with a thickness of 1 μI was formed by sputtering under the following conditions.
was formed.

Target 7: Zno, coo, MgO.

B l z 03 t P r 203 each 0.5m
Baked with 1% o added, spatter pressure crab 2 x 1 O-2 Torr atmosphere
Air: Mixed gas of oxygen and argon Substrate temperature: 350°C Deposition rate: 1 μm/hour RF power: 150 W In addition, a ZnO thin film (1 μm
The current-voltage characteristics of m) were similar to those in FIG.

Next, in the same manner as in Example 1, an AQ set of electrodes was formed to create an EL element.

When an alternating current pulse voltage was applied to this EL element at 5 KHz and the EL characteristics were examined, it was found that, as shown in FIG. 4, when the driving voltage was about 100 V, the luminance was substantially saturated and stable light emission was achieved. Furthermore, as the voltage was further increased, self-healing dielectric breakdown occurred.

Example 3 ZnO:AQ transparent 11! was deposited on a glass substrate by sputtering. The poles are formed using a thin film of 1000 people. in addition,
S by ion blating under the same conditions as Example 2.
rTi○, an insulating layer was formed to a thickness of 2000 mm.

On this insulating layer, the substrate temperature is 450°C by co-evaporation method.
A 5rSe:Ce light-emitting layer with a thickness of 1 μm was formed.

On this light emitting layer, a 5rTi*3 insulating layer was again formed in the same manner as above.

Furthermore, on this insulating layer, a ZnO layer (non-ohmic electrically conductive layer) with a thickness of 1 μm is formed by sputtering under the following conditions.
was formed.

Target: Co O+ M g O+ B i on Zn○
20. ．． 5b203. MnO.

Cr2O, each added (1.5 mo1%) and fired. Sputter pressure crab 2 x 10"" Torr atmosphere.
Air: Mixed gas of oxygen and argon Substrate temperature: 350°C Deposition rate = 1 μm/hour RF power: 150 W In addition, a ZnO thin film (1μ
The current-voltage characteristics of m) were similar to those in FIG.

Next, an AQ electrode was formed on this ZnO layer in the same manner as in Example 1 to produce an EL element.

It was found that the luminance of this EL element was approximately saturated at a driving voltage of about 120 W, and stable light emission was achieved. Furthermore, as the voltage was further increased, self-healing dielectric breakdown occurred.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the configuration of an EL element. FIG. 2 is a graph showing current-voltage characteristics of a ZnO thin film. FIGS. 3 and 4 are graphs showing the voltage-luminance characteristics of the EL strings of the examples. 11...Transparent substrate 13...Transparent electrode 15.
...First insulating layer 17...Light emitting layer 19...Second
Insulating layer 21...Non-ohmic electrically conductive layer 23...Back electrode Fig. 1 Fig. 2 Fig. 3 Fig. 4
op)

Claims (1)

[Claims] 1. An electroluminescent element comprising a light emitting layer that emits light when an electric field is applied, a back electrode and a transparent electrode for applying an electric field to the light emitting layer, and an insulating layer provided between at least the light emitting layer and the back electrode. An electroluminescent device according to claim 1, further comprising a thin layer exhibiting non-ohmic electrical conduction between the insulating layer and the back electrode.