JPH0256898A - Electroluminescence element - Google Patents

Abstract

PURPOSE:To prevent the excitation breakdown of a luminous layer due to an overcurrent by improving the material of MnO2 and using a current limiting layer with preferable resistivity for a hybrid type electroluminescence EL element. CONSTITUTION:A transparent electrode 2, a luminous layer 3, a current limiting layer 4 fixed with conducting fine powder by a binder, and a back electrode 5 are provided on a transparent insulating base 1. A mixture of alpha type MnO2 and gamma type MnO2 or delta type MnO2 is used as the conducting fine powder of the current limiting layer. The resistivity of the current limiting layer of a hybrid type EL element can be set to the optimum value in the range of 1X10<4>OMEGA.cm-5X10<5>OMEGA.cm, the breakage of the element due to an overcurrent can be prevented, and an EL display with high reliability can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the structure of an electroluminescent (hereinafter abbreviated as EL) element, and particularly to the material of the conductive fine powder of the current limiting layer. It is something.

[Prior Art] An EL display using an EL element is a promising flat display that is rapidly becoming popular in portable type computer terminals and the like in recent years.

Two types of EL devices are known: thin-film EL devices and powder-type EL devices, but recently hybrid EL devices (also called hybrid EL devices or composite EL devices), which are a combination of thin-film and powder EL devices, have also been developed. , it has come to attract attention as a type of powerful EL element.

FIG. 1 shows the structure of a hybrid EL element. The structure and manufacturing method of the EL element will be explained using this V.

A transparent electrode material such as indium or tin oxide (ITO) is formed as a transparent electrode 2 on a glass substrate 1 by sputtering, vacuum evaporation, or the like. A light emitting layer 3 is formed thereon using a method such as a vacuum evaporation method, a sputtering method, or an MOCVD method. The material of the light emitting layer is ZnS, Z
Mn is added to ■-■ group compounds such as n S e and Cd S.
, Cu, transition metals and Tb.

Those doped with rare earth elements such as Sm and Dy, or their fluorides and chlorides as luminescent centers are often used. On top of that, as a current limiter N4, a powder layer of about several tens of micrometers made of conductive fine powder hardened with an organic binder is formed by a method such as a spray method. Finally, the upper electrode 5
An EL element is completed by forming a film of a metal such as AI by vacuum evaporation or sputtering.

When manufacturing a dot matrix type display panel, patterning is then performed by mechanical scratching using a diamond needle or the like. Therefore, the thickness of the current limiting layer is preferably from 5 μm to 30 μm. .

The current limiting layer 4 serves to prevent the resistivity of the light emitting layer from decreasing during light emission and excessive X current to flow through the EL device, thereby preventing the device from being thermally destroyed. The larger the resistance of the current limiting layer, the more stable it will be against breakdown, but if it is too large, the voltage drop in the current limiting layer will increase, which will lead to
Since this leads to an increase in the driving voltage of the L element, there is a limit of 50 Ω per unit area (lCm2) in the thickness direction in the film thickness range of 5 μm to 30 μm.
The resistance value of 200Ω from , i.e., I
A resistivity of about 5×10 5 Ω·Cm is preferable.

The material of the conductive fine powder needs to have the above-mentioned resistivity after hardening with a binder, so I
It is required to have a resistivity of about 10'Ω"cm to 5X105Ω'cm. Initially, Cu-coated ZnS powder used in powder-type EL devices was often used, but recently black EL devices The contrast of M is improved, and the resistance value does not change over time due to the movement of Cu.
n 02 has come to be used.

[Problem M to be solved by the invention] However, the resistivity of conventionally used Mn02 is about one to two orders of magnitude lower than the resistivity preferable for hybrid EL elements, so this '2M'A limitation There was a problem in that the element used in the layer could not sufficiently limit the current, and local destruction of the light emitting layer was likely to occur.

[Means for Solving the Problems] Therefore, in the present invention, in addition to improving the MnO2 material as described below, the destruction can be improved by using a current limiting layer having a resistivity suitable for a hybrid EL element. Problem solved.

The present invention provides a transparent electrode on a transparent insulating substrate.

In an electroluminescent element including a light emitting layer, a current limiting layer in which conductive fine powder is fixed with a binder, and a back electrode, α-type Mn 02 and γ are used as the conductive fine powder.
It is an electroluminescent device using a mixture of type MnO2 or δ type MnO2.

Conventionally, it has been known to use MnO2 as a conductive fine powder in a current limiting layer of a hybrid EL element.

In general, the phases of M n O2 are roughly divided into α, β, and γ.
They are divided into three types, and their resistivities are usually in the relationship of precipitation γ (106 Ω·am)>α and electrolytic γ (lO2 Ω-cm)>β (10 IΩ·cm) at room temperature.

Among these, electrolytic γ-type M n O2 has a resistivity close to the desired resistivity value mentioned above and is used as a material for dry batteries, so it is widely mass-produced industrially and is stable. Quality powder can be made by hand. Therefore, conventionally, electrolytic γ-type M n O 2 obtained by electrolyzing a mixed solution of MnCO 3 , H 2 SO 4 , and limestone has been mainly used as the conductive material for N in the EL element and the flow restriction layer.

The present invention was developed in view of the problems of conventional EL devices that use only electrolytic γ-type M n O 2 as the conductive material for the current limiting layer of the EL device.

The first method of the present invention is to use α-type M n O2 and γ-type M
This method uses a mixture of nO2. α-type MnO2
and γ-type M n O2 alone exhibit X-ray diffraction patterns as shown in FIG. 2, respectively. Therefore, α
The X-ray diffraction pattern of the mixture of type M n O2 and γ type MnO2 is a combination of the above two diffraction patterns. The conductivity can be controlled by changing the ratio of the α type and the γ type, and the ratio can be quantitatively evaluated to some extent from the ratio of the peak intensities of X-ray diffraction.

FIG. 3 shows peak intensity ■α of 1,55×10-”m, which is a characteristic X-ray diffraction peak of α-type MnO2 in a mixture of α-type MnO2 and γ-type MnO2.

1°4, which is the characteristic X-ray diffraction peak of γ-type Mn 02
Ratio of peak intensity Iγ of 0X10-”m ([α/■γ)
FIG.

From this figure, when the peak intensity ratio (Iα/■γ) is between 0.5 and 2, it is preferable for the hybrid EL device.
It can be seen that a resistivity between lXl0'ΩψCm and 5X10SΩ·cm can be obtained.

A mixture of α type and γ type may be obtained by mixing and dispersing powders of each type, or a mixture between α type and γ type! ! It can also be obtained by manufacturing under the same conditions.

The second method of the present invention is a method using δ-type M n O2. As shown in FIG. 2, this M n O2 is
&1 In diffraction, the interplanar spacing is 1. 42 x 10-”m.

2., 44XIO-"m, 3. It has peaks corresponding to 66X10-th and 7°28X10-", and its crystal structure has characteristics similar to α-type MnO2, which has a poor crystal structure.

However, due to poor crystallinity, the conductivity is lower than that of the conventional α-type M.
It is possible to achieve a resistivity between 1Xl0'Ω'cm and 5X105Ω·cm, which is lower than nO2 and is preferable for hybrid EL devices.

The above α-type MnO2, γ-type MnO2 and δ-type MnO
2, for example, K M n O4 and a large amount of MnSO4,
It can be obtained by reacting large amounts of KMnO4 and MnSO4, and KMn04 and HCt, respectively.

[Function] That is, the present invention suppresses local destruction of the light-emitting layer that occurs in conventional hybrid EL devices due to inadequate resistivity of the electrolytic γ-type M n 02 that has been used as the conductive fine powder of the current limiting layer. The decision was made in view of the fact that
The conductive fine powder of the current limiting layer used in the present invention is α-type M n
A mixture of O2 and γ type M n O2 or δ type M n
It is O2.

As conductive fine powder, α type M n O2 and γ type M n
By using a mixture of
It is possible to set the optimum value between 'Ωcm to 5×10'Ω·cm, prevent destruction of the element due to excessive current, and obtain a highly reliable EL display.

[Examples] Example 1 ITO was formed as a transparent electrode on a glass substrate to a thickness of about 500 nm using reactive sputtering, and then patterned into a predetermined shape using photolithography. Next, Zn doped with 0.3% Mn was used as a light emitting layer.
A film of about 1 μm of S was formed using an electron beam evaporation method.

Next, a paint in which δ-type MnO2 powder was dispersed in a mixture of binder resin and thinner was applied by spraying and dried to form a current limiting layer with a resistivity of lXl0'Ωcm and a film thickness of 16μm. Formed.

Next, as a back electrode, an AI film was formed to a thickness of about 1 μm by vacuum evaporation, and then the current limiting layer and the AI film were simultaneously scribed using a diamond needle to form a predetermined back electrode pattern.

The number of electrical breakdowns per cm2 of the ELW element thus produced was 0. There is one,
E using conventional γ-type MnO2 powder in the current limiting layer
LS: Significantly improved compared to the child's 5 items.

Example 2 ITO was formed as a transparent electrode on a glass substrate to a thickness of about 500 nm using reactive sputtering, and then patterned into a predetermined shape using photolithography. Subsequently, Zn doped with 0.3% by weight of Mn was used as a light emitting layer.
A film of approximately 1 μm1 of S was formed using electron beam evaporation.

Next, a mixed powder of α-type MnO2 and γ-type Mn02 (l, which is the characteristic peak of α-type Mn02 in X-ray diffraction).

The peak intensity Ia of 55X10-1em and the same γ-type MnO
1, which is the characteristic peak of 2, 40X 10-”m
The ratio of the peak intensity Iγ of
A current limiting layer of Ω·cm and a film thickness of 15 μm was formed.

Next, as a back electrode, a film of AI was deposited to a thickness of about 1 μm by vacuum evaporation, and then the current limiting layer and the A1 film were simultaneously scribed using a diamond needle to form a predetermined back electrode pattern.

Electricity per 1 cm2 of the EL element fabricated in this way @
The number of broken down is 0.05
This is a significant improvement over the conventional EL device using γ-type M n O2 powder in the current limiting layer.

[Effects of the Invention] According to the present invention, in a hybrid EL device using + M n O2 in the current limiting layer, the resistivity of the current limiting layer is set to f between 1×10 −Ω·cm and 5×10 5 Ω·cm. #
It becomes possible to set the weekly value, and it is possible to prevent damage to the luminescent layer due to excessive current. As a result, M
In addition to nO2's low cost, (1) high contrast, (2) long life properties, and (2) extremely high reliability against current damage, it is possible to realize a hybrid EL element.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing a hybrid EL element of the present invention;
Figure 2 shows δ-type MnO2, α-type MnO2゜γ-type Mn
Figure 3 shows the X-ray diffraction patterns of O2 and a mixture of α-type MnO2 and γ-type MnO2.
X-ray diffraction α form M n in a mixture of type M n 02
1,55X 10-11 which is the characteristic peak of O2
The peak intensity Ta at 1m and the peak intensity Iγ at 1,40X10-1θm, which is a characteristic peak of the same γ type Mn 02.
FIG. 2 is a diagram showing the relationship between the ratio (Iα/■γ) and conductivity. 1. Glass substrate 2. Transparent electrode 3, light emission @4. Current limiting layer 5, back electrode Fig. 1 2θ Fig. 2

Claims (1)

[Claims] (1) In an electroluminescent device in which a transparent electrode, a light emitting layer, a current limiting layer in which conductive fine powder is fixed with a binder and a back electrode are provided on a transparent insulating substrate, α-type MnO_2 is used as the conductive fine powder. and γ-type MnO_2
An electroluminescent device characterized by using a mixture of or δ-type MnO_2.