JPH01260796A - Electroluminescent element - Google Patents

Abstract

PURPOSE:To prevent the rapid increase of the current due to the temperature rising of an electroluminescent element so as to prevent the breakdown of which by using a mixture of powder of two components as an inorganic resistant powder constructing the current limiting layer of the element and minimizing the temperature dependency of the electric resistance of one component of larger electric resistance than the other component. CONSTITUTION:An electroluminescent element is constructed with a transparent electrode 2, a layer 3 consisting of luminescent material, a current limiting layer 4 and a rear electrode 5 piled up successively on a transparent substrate 1. The current limiting layer 4 of the EL element is made of a mixed powder of [a] manganese oxides selected from the group consisting of manganese monoxide and manganese 4-3 oxide and [b] compounds and/or elements selected from the group consisting of manganese 3-2 oxide, beta-manganese dioxide, carbon black, and elements of the groups Ib, IIb, IIIb excluding boron, IV excluding carbon and silicon, V excluding nitrogen, phosphor and arcenic, VIa, VIIa and VIII, and is solidified with binder resin. Thereby the brightness ununiformity of the EL elements can be improved and the breakdown can be prevented to improve the reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] - The present invention relates to an electroluminescent device (hereinafter abbreviated as an EL device), and particularly to an EL device useful for a direct current light emitting type EL display device.

[Conventional technology]

In recent years, with the spread of computers, the demand for display devices has increased, and in particular, there is a movement to improve the thickness of CRTs (curvature tubes), which are currently widely used. It's thriving. Typical flat display devices that have now reached the stage of practical use include LCD (Liquid Crystal Display), P.
There are four types: D (plasma display), ELD (electroluminescent display), and fluorescent display tube.
Among them, ELD stands out in terms of high brightness, good contrast, and wide viewing angle.

However, the ELDs currently in mass production are double-insulated.
This type of structure has many layers of thin films formed by vacuum deposition, and the yield when forming each layer is not very high, making it extremely difficult to improve the overall yield. It is.

However, with ELDs that are currently under development and emit light by passing a direct current through them, the thickness of the layer provided in order to limit the direct current is increased to reduce the possibility of pinhole formation (and increase the yield). Is possible.

The currently known structure of this type of ELD is as shown in Figure 1, in which a transparent electrode is formed on a glass substrate, and a light emitting layer, a current limiting layer, and a back electrode are sequentially formed on the transparent electrode. (For example, British Patent GB217634OA) Compared to the double insulation type, since neither of the two insulation films formed by vacuum film formation is used, the yield is higher and the cost is lower.

[Problem to be solved by the invention]

However, in the conventional EL element described above, the electrical resistance of the current limiting layer rapidly decreases due to the temperature rise due to light emission.
There is a serious problem in that the vicious cycle of heat generation due to the flow of even larger currents causes uneven brightness and shortened lifespan.

[Means to solve the problem]

The present invention has been made in order to solve the above-mentioned conventional problems, and includes a transparent electrode 9 and a layer made of a luminescent material on a transparent substrate.

In an electroluminescent device formed by sequentially laminating a current limiting layer and a back electrode, the current limiting layer is formed by: a. at least one manganese oxide selected from the group consisting of manganese monoxide and trimanganese tetroxide, and b. Manganese sesquioxide, beta manganese dioxide, carbon black, Ib group, nb group, excluding boron < nrb group, ■ group excluding carbon and silicon, V group excluding nitrogen, phosphorus, arsenic, ■ a group, VIa group A mixed powder of at least one compound and/or element selected from the group consisting of each element of group (1) is fixed with a binder resin.

First, the materials of Group 31 are materials with a specific resistance of 10 &Ω·low order, and this does not change or changes only slightly with an increase in temperature. By the way. The specific resistances of manganese monoxide and trimanganese tetroxide near room temperature are 1.5×10hΩ・(2) and 2.3X, respectively.
10hΩ・1.5×10' at around 100℃
Ω・mouth and 2.0×10bΩ・mouth.

Next, the substances in the 0 group have a lower resistivity than the substances in the 31 group. For example, manganese sesquioxide and beta-type manganese dioxide each have a resistivity of 5 x 102 ohms and 7 x 10' ohms at room temperature, respectively. has. Further, carbon black has a fairly wide range of resistivity values, centered around 10-1 Ω·(maximum). In addition to these, many other metals or metalloids have relatively low resistivities.

Group Ib elements (Memphreyev periodic table, same below) are:
These are copper, silver, and gold, and the MB group element is zinc.

Group IIIb elements, excluding boron, include cadmium and mercury, and include aluminum, gallium, and indium.

Thallium is group II elements excluding carbon and silicon, which include titanium, zirconium, hafnium, germanium,
These are tin and lead, and group II elements excluding nitrogen, phosphorus, and arsenic are vanadium, niobium, tantalum, antimony, and bismuth. Group Vi elements are chromium, molybdenum, and tungsten, and group VIa elements are , manganese, technetium, and rhenium, and group Ⅰ elements are iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum.

All of the above current limiting layer constituents are used in powder form, and these are fixed using a binder resin. As the binder resin, ordinary organic polymer substances and silicone resins can be used.

Examples of these include vinyl resins, polyester resins, polyamide resins, polyimide resins, cellulose resins, polyurethane resins, urea resins, epoxy resins, melamine resins, silicone resins, etc. In particular, polymeric materials having polar groups are preferably used.

Examples of polymeric materials with polar groups include vinyl alcohol, acrylic acid, methacrylic acid, copolymers with N,N-dimethylaminomethacrylate residues, polyurethanes and silicone resins containing polyols in excess of the equivalent amount. Can be mentioned.

These can be used alone or as a mixture.

The average particle diameter of the powder bound using these binder resins is preferably 10 nm to 10 μm, more preferably 1100 nm to 3 μm.

When the particle size is smaller than 10 nm, the ratio of surface atoms of the powder becomes too large, making it difficult to obtain the original properties, and when the particle size is larger than 10 μm, it tends to cause a decrease in dispersibility and uneven film thickness.

Further, the electrical resistance of the powder is preferably 4 to 4 x 10'Ω・C, and the mixing ratio of component a having a resistivity exceeding this range and component a having a lower resistivity is adjusted. This achieves the above range. In this case, the resistivity of component a, which has a larger resistivity, does not change much even when the temperature changes, so if component a, which has a lower resistivity, is added to it to prepare a product in the above range. , the temperature dependence of the electrical resistance can be reduced. The mixing ratio of the mixture of a and b is a:b
(weight ratio) is preferably 1:9999 to 1:999, and by setting such a mixing ratio, it is easy to set the specific resistance of the mixture to 4 to 4×10 5 Ω·■.

If the a:b (weight ratio) is smaller than 1:9999, the effect of the present invention will not be apparent.
Luminance unevenness is likely to occur due to uneven thickness of the current limiting layer.

Each of the above groups a and b may be a mixture of powders each having a single component, or may be a powder of an alloy, a mixed oxide, or the like.

Further, the mixed powder of a and b may be a mixture of powders of individual components of groups a and b, or may be a powder of compounds of groups a and b, or a powder of a mixture.

If the thickness of the current limiting layer is less than 1 μm, the powder particles will become larger than the film thickness, impairing the uniformity of electrical resistance, and if it exceeds 100 μm, the film will tend to crack and become unstable. Become. A more preferable film thickness is 5 to 20 μm.

[For production]

In the present invention, breakdown due to heat generation of the conventional current limiting layer is caused by α used in the current limiting layer.

This is considered to be caused by the characteristics of γ- or δ-type manganese dioxide,
According to the present invention, a mixture of two component powders is used as the inorganic powder serving as the resistor constituting the current limiting layer, and the temperature dependence of the electrical resistance of the component having the higher electrical resistance is reduced. Therefore, the temperature dependence of the electrical resistance of the current limiting layer is also reduced, preventing a sudden increase in current due to the temperature rise, and preventing breakdown of the EL element.

Example Examples 1-6 ■ Preparation of paint First, paints A to (2) were each prepared according to the following procedure.

Paint A - Manganese oxide 0.7gt - 25% of nitrocellulose
Methyl ethyl ketone (hereinafter abbreviated as MEK) solution 20
0g and ethyl acetate/toluene = 1/1 solvent 1500g
The mixture was milled with a ball mill for 2 hours to ensure uniform dispersion.

Paint B 0.7g of trimanganese tetroxide and 25% of acetylcellulose
%MEK solution 200g and ethyl acetate/toluene = 1/1
milled in a ball mill for 2 hours with 1500 g of solvent,
Evenly dispersed.

Paint C: Add 0.4 g of trimanganese tetroxide to 2 of polyvinyl butyral.
200g of 5% MBK solution and ethyl acetate/toluene = l/
Milled in a ball mill for 2 hours with 1500 g of the solvent of 1,
Evenly dispersed.

Paint D 1 kg of carbon black, 200 g of MEK solution of nitrocellulose, and solvent 1 of ethyl acetate/toluene = 171
Milled with 500 g in a ball mill for 2 hours to uniformly disperse.

Paint E A uniformly dispersed paint was obtained in the same manner as in the case of paint except that antimony powder was used instead of carbon black.

Paint F A uniformly dispersed paint was obtained in the same manner as in the case of paint except that silver powder was used instead of carbon black.

Paint G A uniformly dispersed paint was obtained in the same manner as in the case of paint except that germanium powder was used in place of the carbon blank.

Paint H A uniformly dispersed paint was obtained in the same manner as in the case of paint, except that titanium powder was used instead of carbon black.

Paint 1 A uniformly dispersed paint was obtained in the same manner as in the case of paint, except that nickel powder was used instead of carbon black.

■ Fabrication of EL nacelle Next, indium tin oxide (ITO) is formed into a film by sputtering on a transparent insulating substrate 1 such as a glass substrate, and then buttered by photolithography to form comb-shaped electrodes 2 (transparent electrodes). After coating, a manganese-doped ZnS film 3 (emissive layer) is deposited using a vacuum evaporation method with a thickness of about 500 ml.
A film with a thickness of nm was formed.

A and D (Example 1), A and E (Example 2), A and F (Example 3), and B and G (Example 4) in a 1:1 weight ratio of paints A to ■. .
After that, an aluminum film with a thickness of about 10 μm was formed on top of it by vacuum evaporation method, and the current limiting layer and aluminum layer were scraped off together with the ITO pattern by scratching with a needle perpendicular to the ITO pattern to form a CL type. A back electrode 5 was formed and sealed.

When the dot-to-trimmed EL panel produced as described above was connected to a drive circuit and emitted light, it emitted light uniformly from the front surface, and no unevenness in brightness was observed.

Comparative Example 1 Trimanganese tetroxide. 10 g each of manganese monoxide, carbon black, and silver powder, 2 g of nitrocellulose
4g of 5% MEK solution and ethyl acetate/toluene = 1/1
Four types of paints were prepared by adding and dispersing them to 30g of solvent, and using these, an EL nacelle was created in the same manner as in the example, and an attempt was made to connect it to a drive circuit to emit light, but no light was emitted at all. There wasn't.

Comparative Example 2 An EL nacelle was produced in the same manner as in Comparative Example 1 using α-manganese dioxide and T-manganese dioxide.

-6 luminescence was observed, but the brightness unevenness that was initially observed gradually became larger as time passed, and eventually breakdowns occurred in places.

〔Effect of the invention〕

According to the present invention, it is possible to improve the brightness unevenness of an EL element using a current limiting layer, prevent breakdown, and improve the reliability of the EL element.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing an electroluminescent device manufactured in an example.

Claims (2)

[Claims] (1) An electroluminescent device comprising a transparent electrode, a layer made of a luminescent material, a current limiting layer, and a back electrode laminated in sequence on a transparent substrate, wherein the current limiting layer comprises: a. at least one manganese oxide selected from the group consisting of manganese monoxide and trimanganese tetroxide, and b. Manganese sesquioxide, beta manganese dioxide, carbon black, and Group Ib, , IIb, Group IIIb excluding boron, Group IV excluding carbon and silicon, Group V excluding nitrogen, phosphorus, arsenic, and VIa.
1. An electroluminescent element comprising a mixed powder of at least one compound and/or element selected from the group consisting of elements of Group VIIa and Group VIII, fixed with a binder resin. (2) The mixing ratio of a in the mixed powder is 0.01 to 0.
2. The electroluminescent device according to claim 1, wherein the amount is 1% by weight.