JPH0224995A - Electroluminescence element - Google Patents

Abstract

PURPOSE:To make electric field resting on a phosphor layer uniform so as to improve brightness, in an EL element where a phosphor layer and a dielectric layer are provided between a transparent electrode and a rear electrode, by providing an insulating film consisting of oxide or nitride whose dielectric constant is specified beforehand between the transparent electrode and the light emitting layer in the specified width. CONSTITUTION:When providing a transparent electrode 2 consisting of an ITO film on a transparent substrate 1 such as polyethylene terephthalate, etc., and forming a phospherlayer 4 thereon, those are done as follows. That is, an insulating film 3 consisting of oxide or nitride whose dielectric constants is below 25 is provided beforehand between the electrode 2 and the light emitting layer 4 in the thickness of 5 to 10000nm. Thereafter, a dielectric layer 5 is formed on the light emitting layer 4, and is covered with a rear electrode 6, and these contents are sealed with armors 7 whose ends are fixed with adhesives 8. Since the insulating film 3 whose dielectric constant is small and whose thickness is thin are put between the electrode 2 and the light emitting layer 4 this way, unequal electric field is not applied to a phosphor which constitutes the light emitting layer 4, and the brightness improves.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to electroluminescent devices.

[Conventional technology]

In the dispersion type electroluminescent device, the light emitting layer is made of a mixture of a phosphor and a binder, and as shown in FIG. 3, the light emitting layer 4 is formed directly on the transparent electrode 2 (
For example, Japanese Patent Application Laid-Open No. 57-80695).

[Problems to be Solved by the Invention] However, in the above electroluminescent device, since the dielectric constant of the phosphor and the dielectric constant of the binder are different, a non-uniform electric field is applied to the phosphor, resulting in a problem of low brightness. there were.

As described above, the present invention solves the problem that in conventional electroluminescent devices, a non-uniform electric field is applied to the phosphor, resulting in a reduction in brightness. The purpose is to provide

[Means to solve the problem]

The present invention provides an insulating thin film made of an oxide or nitride with a dielectric constant of 25 or less between the transparent electrode and the light emitting layer.
By providing the phosphor with a thickness of 0.00 nm, it is possible to prevent a non-uniform electric field from being applied to the phosphor, thereby making it possible to exhibit high brightness.

That is, by providing an insulating thin film made of the above oxide or nitride between the transparent electrode and the light-emitting layer, the electric field applied to the light-emitting layer is regulated by the insulating thin film, and the phosphor is Based on the difference between the dielectric constant and the dielectric constant of the binder, a non-uniform electric field is prevented from being applied to the phosphor, and a uniform electric field is applied to the phosphor, so that the electroluminescent device exhibits high brightness. become. In addition, the insulating thin film prevents contact between the phosphor and the transparent electrode, and prevents excessive current from flowing at the contact area between the phosphor and the transparent electrode during light emission and reducing luminous efficiency. Brightness also improves.

Next, the structure of the electroluminescent device of the present invention will be explained with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of an electroluminescent device according to the present invention. In FIG. 1, 1 is a transparent substrate, 2 is a transparent electrode, and 3 is an oxide or nitride with a dielectric constant of 25 or less. It is an insulating thin film, 4 is a light emitting layer, 5 is a dielectric layer, 6 is a back electrode, 7 is an exterior body made of a moisture-proof film, and 8 is an adhesive. Although not shown in FIG. 1, lead bodies are drawn out from the transparent electrode 2 and the back electrode 6, respectively, so that they can be connected to an external drive power source.

For example, a polyethylene terephthalate film with a thickness of about 10 to 50 μrn is used for the transparent substrate I, and the transparent electrode 2 is made of an indium-tin oxide film (hereinafter referred to as an ITO film), which is formed on the transparent substrate I by a vacuum evaporation method. It is formed by a sputtering method or the like.

The insulating thin film 3 is made of an oxide or nitride with a dielectric constant of 25 or less, as will be exemplified later, and the light emitting layer 4 formed on the transparent mold 8i2 by vacuum evaporation or sputtering is made of a phosphor. It consists of a mixture with a binder, and the phosphor is ZnS as a matrix, and Cu, CI, Cu, AI,
Those to which activators such as Cu and Mn are added are used, and high dielectric constant organic substances such as cyanoethylated cellulose and cyanoethylated pullulan are used as binders. The dielectric layer 5 is made of a mixture of a high dielectric constant oxide such as BaTiOz and a binder made of a high dielectric constant organic substance such as the aforementioned cyanoethylated cellulose or cyanoethylated pullulan. The light-emitting layer 4 and the dielectric layer 5 are schematically shown in enlarged form as shown in FIG. 2. Based on FIG. The phosphor 4a is dispersed in a binder 4b made of a dielectric constant organic substance, and in the dielectric layer 5, BaTi0. High dielectric constant oxides 5a such as oxides 5a are present in a dispersed manner. In this way, in the light-emitting layer 4, the phosphor 4a is dispersed in the binder 4b, so as shown in FIG. In an electroluminescent device, there is a drawback that a non-uniform electric field is applied to the phosphor 4a due to the difference between the dielectric constant of the phosphor 4a of the light emitting layer 4 and the dielectric constant of the binder 4b, resulting in low brightness. In this electroluminescent device, since the insulating thin film 3 is provided between the transparent electrode 2 and the light emitting layer 4, the electric field applied to the light emitting layer 4 is regulated by the insulating thin film 3, and a non-uniform electric field is generated on the phosphor. This is prevented,
A uniform electric field will be applied to the phosphor, and the electroluminescent device will exhibit high brightness. Furthermore, as shown in FIG. 3, in an electroluminescent element with a conventional structure in which a light emitting layer 4 is directly formed on a transparent electrode 2, since the phosphor and the transparent electrode 2 are in contact with each other, the fluorescent material emits light when emitting light. However, in the electroluminescent device of the present invention, the transparent electrode 2 and the light emitting layer 4
Since the insulating thin film 3 is provided between the phosphor and the transparent electrode 2, there is no contact between the phosphor and the transparent electrode 2. Therefore, when emitting light, an excessive current flows in the contact area between the phosphor and the transparent electrode 2, reducing luminous efficiency. The brightness is improved from this point of view as well.

The back electrode 6 is made of an aluminum vapor-deposited film with a thickness of 100 to 500 nm formed on an aluminum foil with a thickness of about 50 μm or a polyethylene terephthalate film with a thickness of 10 to 50 μm. A polychlorotrifluoroethylene sheet of about 500 am is used.

Element contents such as the transparent substrate 1, the transparent electrode 2, the insulating thin film 3, the light emitting layer 4, the dielectric layer 5, and the back electrode 6 are covered with the exterior body 7 made of the moisture-proof film.
The joints between them are bonded with an adhesive 8, so that the inside of the element is sealed.

The material constituting the insulating thin film 3 is made of oxide or nitride, and these oxides or nitrides have a dielectric constant of 2.
The oxide constituting this insulating thin film 3 is preferably one having a dielectric constant of 5 or less, particularly in the range of 3 to 20.
For example, AI! 0ff (relative permittivity 8), Ta5ks (
Relative permittivity 25), YgCh (relative permittivity +5), S
iOx (relative permittivity 5), etc. are used, and examples of nitrides include AIN (relative permittivity 8), s13N4
(relative dielectric constant 5), etc. are used. The insulating El film 3 made of these oxides or nitrides is formed on the transparent electrode 2 by a vacuum evaporation method, a spunter method, etc., and has a thickness of 5 to 1.0
It needs to be in the range of 00 nm, especially in the range of 10 to 3
00 nm range is preferable, that is, the above insulating thin film 3
When the thickness of the insulating thin film 3 becomes thinner than 5 nm, the effect of making the electric field applied to the phosphor uniform becomes less.
．． When the thickness exceeds 000 nm, the luminescent state of the phosphor becomes more visible from the outside due to the increased thickness, and the dimensional stability decreases.

In the present invention, the dielectric constant of the oxide or nitride used to form the insulating thin film 3 is specified to be 25 or less because
When the relative permittivity increases, the electric field applied from the transparent electrode 2 to the light emitting layer 4 is reduced by a thin insulator II! 43, and considering the decrease in coverage due to the increase in thickness, the upper limit of the film thickness that can be formed is about 1,000 nm. This is because it is necessary to keep the

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 A transparent electrode was formed by forming ITOIQ with a thickness of 200 nm by vacuum evaporation on a polyethylene terephthalate film with a thickness of 50 μm as a transparent substrate, and samples N1111 to I- A1□0. of each film thickness shown in 5. The film was formed by vacuum evaporation.

Next, the above A1□0. A paste for forming a light-emitting layer prepared by dispersing cyanoethylated pullulan, ZnS:Cu, and CI in n-methyl-2-pyrrolidone is applied onto the insulating thin film consisting of the film using a screen printing method, and the paste is dried to form a thick layer. A light emitting layer of 60 μm is formed, and then Ba is deposited on the light emitting layer.
Ti0+ and cyanoethylated pullulan were combined with n-methyl-2-
A paste for forming a dielectric layer prepared by dispersing it in pyrrolidone was applied by screen printing and dried to a thickness of 20 μm.
A dielectric layer was formed, and an aluminum whistle having a thickness of 50 μm was laminated on the dielectric layer to form a back electrode. Then, after connecting the lead bodies to the transparent electrode and the back electrode,
The entire structure was sandwiched between upper and lower moisture-proof films made of polychlorotrifluoroethylene with a thickness of 300 μm, and the joints between the moisture-proof films were sealed with an adhesive to produce an electroluminescent device.

Examples 2 to 6 A1 in Example 1. In place of O, respectively, T a
,0. ．． 5in2, YZ Ox, Si*N4, AI
An electroluminescent device was produced in the same manner as in Example 1 except that N was used and the thickness of the insulating thin film made of these oxides or nitrides was 300 nm.

Comparative example 1 A1□0. An electroluminescent device was produced in the same manner as in Example 1 except that the insulating thin film consisting of the following was not formed.

Comparative Example 2 A1. An electroluminescent device was produced in the same manner as in Example 1 except that the thickness of the insulating thin film made of Ol was changed to 2 nm.

Comparative Example 3 An electroluminescent device was produced in the same manner as in Example 1 except that the thickness of the insulating thin film made of A1□03 was changed to 2,000 nm.

A sine wave of 4001 (z) was applied to each electroluminescent device produced as described above, and the luminance at a voltage of 100 cm was measured. The results are shown in Table 1.

As shown in Table 1, the insulating thin film is 5 to 1,000 nr
The electroluminescent element of the example provided at lγ of n had higher luminance than the electroluminescent element of Comparative Example 1, which corresponds to a conventional product.

[Effects of the Invention] As explained above, in the present invention, by providing an insulating thin film made of an oxide or nitride with a low dielectric constant between the transparent electrode and the light emitting layer, the thickness of the insulating film is 5 to 1,000 nm. By regulating the electric field applied to the light-emitting layer with the insulating thin film, it was possible to prevent uneven electric fields from being applied to the phosphor, thereby increasing brightness.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a sectional view showing an example of an electroluminescent device according to the present invention, and FIG. 2 is a schematic enlarged view of a light emitting layer and a dielectric layer of the electroluminescent device. FIG. FIG. 3 is a sectional view showing a conventional electroluminescent device. 2...Transparent electrode, 3...Insulating thin film, 4...Light emitting layer, 5...Dielectric layer, 6...Back electrode 2...Transparent electrode 3, Insulating thin film 4 Light emitting layer

Claims (3)

[Claims] (1) An electroluminescent element in which at least a light-emitting layer 4 and a dielectric layer 5 are provided between the transparent electrode 2 and the back electrode 6, and the dielectric constant between the transparent electrode 2 and the light-emitting layer 4 is 25 or less. An electroluminescent device characterized in that an insulating thin film 3 made of oxide or nitride is provided with a thickness of 5 to 1,000 nm. (2) The oxides are Al_2O_3, Ta_2O_5, S
At least one selected from iO_2 and Y_2O_3
The electroluminescent device according to claim 1, which is a seed. (3) An electroluminescent element in which the nitride is at least one selected from AIN and Si_3N_4.