JPH01245085A - Thin film el element - Google Patents

Abstract

PURPOSE:To provide a thin film EL element having a luminescent layer expressed by a specific compositional formula, generating light having high color purity, exhibiting steep rise of luminance-voltage characteristic, formable into a film at a relatively low temperature and emitting EL luminance by the application of AC electric field. CONSTITUTION:The objective EL element having a luminescent layer expressed by the compositional formula of Sr1-x ZnxS:Euy (0.05<=x<=0.6, preferably 0.2<=x<=0.45; 0.0005<y<0.015) can be produced by adding ZnS to SrS up to about 34% and doping the mixture with Eu to prepare a luminescent layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides EL (Electrical
The present invention relates to an EL element that emits light (luminescence), and particularly relates to an EL element that emits red light.

(Prior Art) In general, a thin film EL device, as shown in FIG. It has a double insulation structure in which two insulation layers 5 are sequentially formed and a back electrode 6 is further formed thereon.

Currently, a thin film EL element having such a structure using ZnS as the base material of the light emitting layer is in practical use. Furthermore, in recent years, with the aim of making EL devices multicolored, EL devices with light-emitting layers made of alkaline earth metal sulfides such as CaS and SrS as base materials have been developed.
The device is attracting attention, and materials for the light-emitting layer that emit red light include ZnS:Sm and C5CaS:
Eu.

S rS: Eu etc. are mainly studied. However, although the EL element having the ZnS:Sm,C light-emitting layer achieves high luminance, the luminance-voltage characteristic has a poor rise.
There is a problem of high power consumption, and CaS: E
EL elements with a u-emitting layer have good brightness-voltage characteristics and are extremely good in terms of color purity, but in order to obtain high brightness, vapor deposition is required at a base temperature of 600°C or higher.
It is difficult to form a large-area thin film like an EL display, and furthermore, although the EL hydrogen atomic brightness-voltage characteristic with the SrS:Eu light-emitting layer has a good rise, the emitted light color is almost orange, and it is difficult to obtain high brightness. The method requires vapor deposition at a substrate temperature of 500° C. or higher, and there is a problem that the device is easily broken when manufacturing the EL device, so it has not been put into practical use at present.

(Problems to be Solved by the Invention) An object of the present invention is to emit red light with good color purity and have a luminance of -
The EL hydrogen element has a light-emitting layer that has good voltage characteristics and can be formed at a relatively low temperature.

(Means for Solving the Problems) In order to solve the above problems, the inventors of the present invention conducted extensive studies and found that ZnS was solidly dissolved in SrS up to about 34%.
If a light-emitting layer is prepared by doping Eu with a composition before or after that and EL hydrogen atoms are created, good light-emitting properties can be obtained even if the film is formed at a relatively low temperature, and an appropriate Z n S jQ
The present invention was completed based on the discovery that highly pure red light corresponding to the red color of a CRT can be obtained at high temperatures.

That is, the present invention includes a light-emitting layer whose composition formula is SrZnS:Euy1-Xx (0.05≦X≦0.6°0.0005<y<0.015). This is a thin film EL device with special features.

As shown in FIG. 1, the thin film EL cable of the present invention is made of InO, SnO2, ITOSZnO:
A transparent electrode 2 such as A1 is formed, and Y O, TiO, 5iNsA l O, S LA
10 N SS t O2, Ta O, SrTiO3
A single or multilayer first insulating layer 3 is formed, and a light emitting layer 4 of SrZnS:Eu is formed on top of the first insulating layer 3, a second insulating layer 5 made of the same material as the first insulating layer 1-Xx, Back side γU of A etc.
An example is one composed of six poles.

Sr Zn S:1- in the EL cord of the present invention
X X In the Eu light-emitting layer, when X is 0.34 or less, the
0% ZnS is dissolved in SrS, and above that, excess Zn
In the region where nS phase separation occurs and X is larger than 0.6,
Since the amount of separated ZnS increases significantly, the light emitting characteristics deteriorate. On the other hand, when X is 0.05 or less, the effect of improving brightness is small. In this region, it emits red light, which is almost the same as the red color of a CRT, and has the highest brightness. A more preferable range is 0.2≦X≦0.45.

Further, when NY of the doped Eu is 0.0005 or less, the light emission of the light emitting layer becomes weak, and when it is 0.2 or more, the light emitting characteristics tend to deteriorate.

The light-emitting layer in the EL element of the present invention is prepared by a vapor deposition method, a sputtering method, an MOCVD method, an ALE method, etc., using Eu, SrS, and ZnS. Temporary temperature 1
It is preferable to prepare a thin film by a vapor deposition method or a sputtering method while maintaining the temperature at 50° C. or more and 400° C. or less, since ZnS is sufficiently dissolved in ZrS and a light emitting layer having excellent light emitting properties can be obtained. Furthermore, if the luminescent layer after preparation is heat-treated at 500° C. or higher in vacuum or in an inert gas atmosphere, the crystallinity of the luminescent layer can be improved and more excellent luminescent properties can be obtained. Further, layers other than the light-emitting layer in the EL hydrogen element of the present invention can be prepared by conventional vapor deposition methods, sputtering methods, MOCVD methods, ALE methods, and the like.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited only to these examples.

Example 1 The EL hydrogen element shown in FIG. 1 was produced by the following procedure.

First, on a glass substrate 1 on which a transparent electrode 2 was patterned, a film of Si At ON composition of 5.5 was deposited.
0.5 0.5 7.5 Using a target, the ratio of A r : N 2 is 3=1
By performing sputtering in a mixed gas of
A first insulating layer 3 having a thickness of 200 nm was prepared.

After that, ZnS was mixed with SrS at 0 to 50 mo1%,
Furthermore, pellets containing 0.2 mo1% of EuS were heated in vacuum with an electron beam and steamed onto the first insulating layer 3 kept at a temperature of 200° C. to prepare a light emitting layer 4 with a thickness of 11000 nm.

Thereafter, heat treatment was performed at a temperature of 650° C. for 1 hour in an Ar gas stream, and then a second insulating layer 5 with a thickness of 200 nm was prepared in the same manner as the first insulating layer 3 described above, and a back surface made of A Electrode 6 was prepared by electron beam evaporation to form a thin film E.
Obtained L.

The Eu6 degree in the light emitting layer of the obtained thin film EL cord is Z n
Even if the Sa degree changed, it was approximately 0.2 mo1%. FIG. 2 shows the change in saturation luminance of the EL element with respect to the ZnS concentration. From Figure 2, the saturation luminance of the EL element is at a ZnS concentration of 34.
It increases up to around m o 196 and rapidly decreases above that point. Figure 3 shows ZnS concentration 31.50mo 1%
The X-ray diffraction pattern is shown. ZnS concentration 31mo1%
Then, the solid solution SrZS of SrS and ZnS (2
A strong −X x orientation of the 00) plane is observed, and the peak intensity due to the separated ZnS is extremely weak. On the other hand, in Zn5a degree 50m01%, Sr
The (200) plane and (111) plane of Sr Z Sr-X x , a solid solution of S and ZnS, are seen, and the (100) plane and (OO2) plane of α-ZnS are also seen as peaks due to separated ZnS. , the separation of ZnS is progressing.

FIG. 4 shows the relationship between the peak intensities of (200), (111), and (002) and the ZnS concentration. The peak intensity of (200) is the highest around x-0,34, and the orientation on this plane is also the strongest, and it is thought that this improvement in orientation contributes to the improvement in the brightness of the EL element. . Also, Zn5(0
Since the intensity of 02) increases significantly when x>0.4,
The rapid decrease in brightness when x > 0.34 is considered to be an effect of phase separation.

In Figure 5! The emission spectrum in the case of −0,33 is shown.

As a comparison, the E of SrS:Eu5CaS:Eu
The red (Y2O2S:Eu) spectra of L and CRT are also shown at the same time. FIG. 6 shows the spectra of the above materials converted into chromaticity coordinates. From Figure 6, x-0,33
In this case, the emitted light color is almost the same as the red of CRT, and CaS
: Inferior to Eu, but superior to SrS:Eu. After further consideration, CR in the area of 0.2≦X≦0.4
It was found that a thin film EL cord that emits red light equivalent to the red color of T can be obtained.

(Effects of the Invention) As described above, the thin film EL device of the present invention is a high-brightness EL device that emits red light equivalent to the red color of a CRT.
In addition, in the film formation process of the light-emitting layer, 150 to 400
A light-emitting layer with excellent light-emitting properties can be obtained at a substrate temperature of °C, and since this temperature is basically low, it cannot be used in ordinary planetary or orbiting dome-type vapor deposition equipment, or large-scale sputtering equipment. It is possible to form a thin film with a large area. In addition, when manufacturing a multicolor EL panel, it is possible to set the substrate temperature in the film formation process of the light emitting layer to 200°C or less, in which case the light emitting layer can be patterned by the lift-off method, and the conditions can be met. Multi-color can be achieved without going through a complicated etching process.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the structure of a thin film EL device of the present invention. FIG. 2 is a diagram showing the relationship between the saturated luminance and the ZnS concentration when the thin film EL device obtained in the example was driven with alternating current at 5 kHz. Figure 3 shows the Z of the light emitting layer of the thin film EL device obtained in the example.
It is a figure which shows the X-ray diffraction pattern at nS7a degree 31.50mo1%. Figure 4 shows the Zn of the light emitting layer of the thin film EL cord obtained in the example.
Solid solution Sr Z Sr-x for 5fi degree
The peak intensities of the (200) and (111) planes of x and α-
FIG. 3 is a diagram showing the relationship between the peak intensity of the (002) plane of ZnS and the Zn concentration. FIG. 5 shows y, - for the thin film EL device obtained in the example.
The emission spectrum in the case of 0.33 and as a comparison,
FIG. 2 is a diagram showing the EL of SrS:Eu5CaS:Eu and the red (Y2O2S:Eu) vector of CRT. FIG. 6 is a diagram showing the chromaticity coordinates of the emission spectra of the materials listed in FIG. 5. In the figure,

Claims (1)

[Claims] (1) A thin film EL device characterized by having a light-emitting layer whose composition formula is Sr_1_-_XZn_XS:Eu_Y (0.05≦x≦0.6, 0.0005<y<0.015) .