JPH04294094A - El element - Google Patents

Abstract

PURPOSE:To provide an EL element, which is equipped with a heightened light emission efficiency, whose manufacturing processes can be simplified to a great extent, and which does not require provision of any barrier layer. CONSTITUTION:The light emitting layer 27 of an EL element consists of a laminate of a plurality of fluorescent substance films 29a-29d, whose mother materials are ZnS and alkali earth metal sulfide, respectively. Among them the fluorescent substance films 29a, 29d whose mother material is ZnS are directly contacted with insulative layers 25, 26 arranged on both main surfaces of the light emitting layer 27.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EL device, and more particularly to an EL device that can improve luminous efficiency and greatly simplify the manufacturing process.

0003

BACKGROUND OF THE INVENTION Various structures of EL elements have been proposed in the past, one of which is proposed by the present inventor in Japanese Patent Application No. 2-173.
An example of the structure of the EL element for color display proposed in No. 320 will be described below with reference to FIG.

The color display EL element 1 shown in FIG.
A light-emitting layer 3 that emits light by an electric field is interposed between a and 2b, and striped electrodes are arranged perpendicularly to each other on both main surfaces of the light-emitting layer 3 via barrier layers 4a and 4b and insulating layers 5a and 5b, respectively. 6a and 6b, matrix display is possible, and furthermore, by arranging a striped color filter 7 between the transparent substrate 2b and the striped electrode 6b on the side of the substrate 2b, the above-mentioned It is configured so that a desired spectral range out of the emission spectrum exhibited by the light emitting layer 3 is extracted.

The light emitting layer 3 of an EL element intended for application to full color display as shown in FIG. 5 is formed by stacking light emitting layers made of light emitting materials corresponding to each of the three primary colors.

At present, ZnS:Tb, in which Tb, which serves as a luminescent center, is doped into ZnS, which serves as a matrix, has been put into practical use as the most promising green luminescent material. Furthermore, SrS:Ce is used as the blue light emitting material, and CaS:Eu is used as the red light emitting material. And EL, which emits white light for the purpose of full-color display.
In the device, the light-emitting layer 3 is formed by laminating three thin films of phosphor containing ZnS and the above-mentioned alkaline earth metal sulfide as base materials.

Barrier layers 4a and 4b are provided on both sides of the light emitting layer 3.
Insulating layers 5a and 5b are formed through the insulating layers, and the material constituting these insulating layers is conventional monochrome TFEL.
Similarly, oxides of metals having a high dielectric breakdown voltage, such as Ta2 O5, Y2 O3 or Al2 O3, are used.

[0008]

[Problems to be Solved by the Invention] However, in an EL element formed by stacking a luminescent layer made of the above-mentioned luminescent material and an insulating layer, a certain type of luminescent layer and an insulating layer may react significantly. , special consideration was required. That is, among various luminescent materials, SrS and Ca
Alkaline earth metal sulfides such as S have chemically unstable properties such as deliquescent properties, and also have properties that easily react with insulating layers formed from oxides. There is a problem in that the stoichiometric composition of the EL element changes over time, significantly reducing the reliability of the EL device. For this reason, barrier layers 4a and 4b made of a substance that does not react with both layers, such as ZnS, AlN, or Si nitride, are provided between the light emitting layer 3 and the oxide insulating layers 5a and 5b. was required.

[0009] The provision of these barrier layers 4a and 4b has a great influence on the performance and manufacturing man-hours of the EL element. That is, when the voltage applied from the outside to the EL element is kept constant, this barrier layer acts as a resistance for electric field formation and reduces the effective electric field formed in the light emitting layer. the result,
This will have a direct negative effect on the luminous efficiency and luminescence start voltage, which are the main performances of the EL element.

On the other hand, forming barrier layers on both sides of the light-emitting layer increases the total number of laminated layers, complicating the manufacturing process and increasing manufacturing costs.

The present invention has been made to solve the above-mentioned problems, and provides an EL that can increase luminous efficiency, greatly simplify the manufacturing process, and eliminates the need to provide a barrier layer. The purpose is to provide an element. [Structure of the invention]

0012

[Means for Solving the Problems] In order to achieve the above object, an EL device according to the present invention includes a light-emitting layer that emits light due to an electric field interposed between a pair of substrates, at least one of which is transparent and disposed facing each other. In an EL element in which electrodes are disposed on both main surfaces of the light emitting layer with an insulating layer interposed therebetween, the light emitting layer is formed by laminating a plurality of phosphor thin films each using ZnS and alkaline earth metal sulfide as base materials. , the phosphor thin film having ZnS as a base material is disposed so as to be in direct contact with the insulating layers disposed on both principal surfaces of the light emitting layer.

[0013]

[Function] According to the EL device having the above structure, ZnS, which does not react with the insulating layer, is added to the insulating layer disposed on both main surfaces of the light emitting layer.
The phosphor thin film with the base material is placed in direct contact with the
Since the structure is such that the phosphor thin film containing alkaline earth metal sulfide as a matrix is isolated from the insulating layer, the chemical stability of the phosphor thin film containing alkaline earth metal sulfide as a matrix is maintained. Therefore, the function of the EL element does not change over time, and the reliability of the element can be significantly improved.

Furthermore, since there is no need to provide a barrier layer between the insulating layer and the light-emitting layer, the thickness of the entire light-emitting layer can be reduced, and the effective electric field formed in the light-emitting layer can be increased. . By increasing the effective electric field, it greatly contributes to improving the performance of EL devices, such as improving luminous efficiency and reducing the emission starting voltage, and also simplifies the manufacturing process of EL devices by omitting the step of forming a barrier layer. , manufacturing costs can be significantly reduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is an exploded perspective view schematically showing one embodiment of an EL element according to the present invention, and is a diagram specifically illustrating an EL element for color display as an example. Moreover, FIG. 2 is a perspective sectional view showing an example of the structure of the light emitting layer shown in FIG.

That is, the color display EL according to this embodiment
As shown in FIG. 1, the element 1a has a light-emitting layer 27 interposed between a pair of substrates 21 and 23, at least one of which is transparent and which is disposed facing each other, and which emits light by an electric field. Matrix display is possible by arranging striped electrodes 24 and 28 perpendicularly to each other with insulating layers 25 and 26 in between, and stripes for extracting a desired spectral range from the emission spectrum exhibited by the light emitting layer 27. The shaped filter 22 is mounted on a transparent substrate 21.
and the striped electrode 22 on the substrate side, and as shown in FIG. In the color display EL element 1a formed by laminating 29a, 29b, 29c, and 29d, Zn
The phosphor thin films 29a and 29d having S as a base material form the light emitting layer 2.
Insulating layers 25 and 26 disposed on both main surfaces of 7 are arranged and configured to be in direct contact with each other.

The substrate 21 is a transparent substrate, and a striped color filter 22 for individually extracting the three primary colors is integrally arranged on the transparent substrate 21. As the material constituting the striped color filter 22, a material having a transmittance distribution suitable for each of the three primary colors is used, regardless of whether it is inorganic or organic.

On the other hand, as the material constituting the transparent substrate 21, glass is generally preferable. However, in cases where the material of the striped color filter 22 is an organic substance, or in cases where the substrate 21 is formed of a polarizing plate to increase contrast, a transparent plastic material may be used.

Further, in FIG. 1, a striped electrode (back electrode) 24 having a high reflectance is disposed on the lower surface of the other substrate 23 facing the transparent substrate 21, and below this striped electrode 24. On the side, a pair of insulating layers 25, 2
A light emitting layer 27 sandwiched between the two substrates 6 is provided.

An insulating layer 2 is formed below the light emitting layer 27 in the figure.
6 in a direction perpendicular to the striped electrode (back electrode) 24, the other striped electrode (transparent electrode) 2
8 are provided, and these orthogonal striped electrodes 24 and 28 enable matrix display.

The light-emitting layer 27 is formed by laminating a plurality of types of phosphor thin films 29a to 29d in which luminescent center elements that emit light of each of the three primary colors are mixed in the matrix. The element serving as the luminescent center is generally selected from rare earth elements.

In particular, in the present invention, the phosphor thin films 29a and 29d are formed into the insulating layers 25 and 25 using ZnS as a base material, which has excellent chemical stability with respect to the oxide insulating layers 25 and 26.
, 26.

That is, as a result of various studies on phosphors having chemical stability with respect to the insulating layer, the present inventors have found that a phosphor having ZnS as a matrix can be used as a light-emitting layer for other monochrome display T.
The above laminated structure was adopted based on the knowledge that it exhibits excellent stability when mounted on an FEL (thin film EL).

On the other hand, the striped electrode (transparent electrode) 28
are formed so as to satisfy the relationship WD≦WF, where the width of one of the striped color filters 22 is WD and the width of one of the striped color filters 22 is WF as shown in FIG. Furthermore, when a desired spectral range is divided into a plurality of parts and extracted, the pitch of the striped color filters 22 and the pitch of the striped electrodes (transparent electrodes) 28 corresponding to each spectral range are formed to be equal.

Note that the opposing substrate 23 is a transparent or non-transparent substrate, and the striped electrodes 24, insulating layers 25, 26, light emitting layer 27,
The portion composed of the striped electrodes 28 has the same structure as a normal double insulation type TFEL element, and these are integrally constructed.

A transparent substrate 21 on which a striped color filter 22 is integrally formed, and a counter substrate on which a striped electrode 24, insulating layers 25, 26, a light emitting layer 27, and a striped electrode 28 are similarly integrated. 23 are in close contact with each other on the film forming surface side to constitute a single light emitting layer electroluminescent section, and the EL element 1 for color display is driven by an alternating current electric field.
a is configured.

Further, the striped color filter 22 and the striped electrode (transparent electrode) 28 on the contact surface are arranged in parallel and regularly and repeatedly facing each other.

[0028] Furthermore, a T
For example, interposing a transparent fluid such as silicone oil to moisture-proof the FEL is effective in improving reliability.

Next, a specific example of the structure of the EL element having the above structure and its evaluation results will be described.

In FIG. 1, a glass substrate is used as the counter substrate 23, and a back electrode 24 made of an aluminum film with a thickness of 120 nm is formed on the glass substrate 23, and is formed into stripes with a width of 2 mm and a pitch of 3 mm. patterned. Next, a layer with a thickness of 470 mm is formed on this back electrode 24.
A first insulating layer 25 of Ta2O5 of 100 nm was coated.

Next, an example of the structure of the light emitting layer 27 will be explained with reference to FIG. FIG. 2 is a partially enlarged perspective cross-sectional view of the light emitting layer 27 in FIG.

That is, a film with a thickness of 15 mm made of ZnS as a matrix and doped with 3% by weight of Tb as a luminescence center element that emits green light.
A 0 nm phosphor thin film 29a was formed on the lower surface of the insulating layer 25. Next, a film with a thickness of 350 nm using SrS as a matrix and doped with 0.5% by weight of Ce as a luminescent center element that emits blue-green light.
A 300 nm thick phosphor thin film 29b is formed on the lower surface of the phosphor thin film 29a, and a 300 nm thick phosphor thin film 29b is formed on the lower surface of the phosphor thin film 29a. A phosphor thin film 29c was formed, and a phosphor thin film 29d having the same composition as the phosphor thin film 29a was further formed on the lower surface side of the phosphor thin film 29c.

Further, on the lower surface of the phosphor thin film 29d, a second insulating layer 2 made of Ta2O5 and having a thickness of 470 nm is formed.
6 and on the lower surface of this second insulating layer 26, as shown in FIG. T. O. A 170 nm thick transparent electrode 28 made of (indium-tin oxide) is formed and patterned into stripes with a width of 2 mm and a pitch of 3 mm so that the transparent electrode 28 is arranged in a direction perpendicular to the back electrode 24. did.

Among the above-mentioned thin films, the insulating layers 25 and 26 and the transparent electrode 28 are formed by magnetron sputtering, while the other thin films are all formed by ordinary double insulation type TF.
It was formed by a vapor deposition method that is used in the formation of EL elements.

On the other hand, a glass substrate was used as the transparent substrate 21, and the formation of the striped color filters 22 on the glass substrate 21 was performed in a separate process. i.e. green,
The blue and red filters were provided in stripes in a periodic manner, each having a width of 3 mm, and were formed in close contact with each other.

[0036] Then, the striped filter 22
And while the transparent electrodes 28 are facing each other in a parallel state, the transparent substrate 21 and the counter substrate 23 are brought into close contact with each other with silicone oil interposed in the gap, while adjusting each pitch,
An EL element 1a for color display was produced.

For the color display EL element 1a thus obtained, an AC voltage of 130 Vrms with a 60 Hz sine wave was applied.
was applied between the electrodes to emit light, and the luminance of the emitted light after passing through the filter was measured. As a result, green is 62nt and blue is 7n.
t and red color were 15 nt, both of which were higher values compared to the conventional example.

FIG. 3 also shows a striped color filter 22.
The emission spectrum in the absence of is shown. FIG. 4 shows the spectral transmittance of each filter.

Next, in order to confirm the stability and durability of the EL element according to the example, the condition of each thin film was observed after the EL element was left for 500 hours. There was no change in the appearance of each thin film. Furthermore, as a result of measuring the luminance of each luminescent color, no significant difference was found between before and after leaving it.

Next, in order to compare the characteristics with a conventional EL element having a barrier layer, in addition to the laminated structure similar to the example,
Between the insulating layer 25 made of Ta2O5 and the phosphor thin film 29a made of ZnS:Tb, and the insulating layer 26 made of Ta2O5
An EL device of a comparative example was prepared by interposing a barrier layer made of AlN and having a thickness of 150 nm between the phosphor thin film 29d made of ZnS:Tb and the ZnS:Tb phosphor thin film 29d.

When the fabricated EL devices of the example and comparative example were operated under the same conditions and their characteristics were compared, the luminous efficiency of the EL device of the example was improved by about 18% compared to the comparative example, and the emission starting voltage was was reduced by about 37%, confirming the excellent characteristics of the EL element of this example.

As described above, the color display E according to this embodiment
For L elements, it has become possible to stack phosphor thin films based on alkaline earth metal sulfides, which are currently the most useful but lack chemical stability, without intervening a special barrier layer. , a stable light-emitting layer can be formed over a long period of time. Therefore, it is possible to obtain an EL element for color display that has excellent performance such as luminous efficiency and luminescence start voltage, is highly reliable, and has low manufacturing cost.

[0043] In the embodiment, color display EL
Although the device has been described as an example, the present invention is not limited thereto, and can be similarly applied to an EL device for monochrome display that has a phosphor thin film and an insulating layer that tend to react with each other. be.

[0044]

[Effects of the Invention] As explained above, according to the EL device according to the present invention, the phosphor thin film whose matrix is ZnS, which does not react with the insulating layer, is in direct contact with the insulating layer disposed on both main surfaces of the light emitting layer. Since the phosphor thin film containing alkaline earth metal sulfide is separated from the insulating layer, the chemical stability of the phosphor thin film containing alkaline earth metal sulfide is maintained. Therefore, the function of the EL element does not change over time, and the reliability of the element can be significantly improved.

Furthermore, since there is no need to provide a barrier layer between the insulating layer and the light-emitting layer, the overall thickness of the light-emitting layer in which TFELs are laminated can be reduced, and the effective electric field formed in the light-emitting layer can be increased. can be done. In addition, by increasing the effective electric field, it greatly contributes to improving the performance of EL elements, such as improving luminous efficiency and reducing the emission starting voltage.
The step of forming a barrier layer can be omitted, the manufacturing process of the EL element can be simplified, and manufacturing costs can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view schematically showing an embodiment of an EL element according to the present invention.

FIG. 2 is a perspective cross-sectional view showing an example of the structure of the light emitting layer shown in FIG. 1;

[Figure 3] TFEL for color display having the structure shown in Figure 1
3 is a graph showing an emission spectrum in the case where there is no color filter in an example of the device.

[Figure 4] TFEL for color display having the structure shown in Figure 1
A graph showing the spectral transmittance of a color filter in an example of the element.

FIG. 5 is an exploded perspective view showing a structural example of a conventional EL element for color display.

[Explanation of symbols]

1, 1a EL element 2a, 2b board 3. Luminescent layer 4a, 4b Barrier layer 5a, 5b Insulating layer 6a, 6b Striped electrode 7 Striped color filter 21 Substrate (transparent substrate) 22 Striped color filter 23　Substrate 24 Striped electrode (back electrode) 25 Insulating layer 26 Insulating layer 27 Luminescent layer

Claims (1)

[Claims] Claim 1: An EL element in which a light-emitting layer that emits light by an electric field is interposed between a pair of substrates, at least one of which is transparent and placed facing each other, and electrodes are arranged on both main surfaces of the light-emitting layer with an insulating layer interposed therebetween. The light-emitting layer is formed by laminating a plurality of phosphor thin films each containing ZnS and an alkaline earth metal sulfide as a base material, and the phosphor thin film containing ZnS as a base material is formed on both main surfaces of the light-emitting layer. An EL element characterized in that the EL element is arranged so as to be in direct contact with an insulating layer disposed on each of the insulating layers.