JPH0467595A - Formation of luminous layer for thin el element - Google Patents

Abstract

PURPOSE:To improve productivity and sharply reduce the cost with only one film forming device by using the EB deposition method in all processes from the first insulating layer to a back electrode. CONSTITUTION:The first thin film serving as the base material of a fluorescent semiconductor material is formed in the first process. ZnS or a mixed crystal of ZnS and CdS is used for the base material, a transparent electrode is provided on the surface of a glass substrate, and an insulating layer is provided on the surface of the electrode for use as the substrate. The second thin film made of an activating agent is overlapped on the surface of the first thin film in the second process. Mn or the like which is an impurity to serve as the luminescence center is doped in the activating agent, and luminescence with different color tone is obtained according to the type. The whole substrate is heated and the activating agent is diffused in the first thin film to form a luminous layer in the third process. Even when multiple second thin films are formed by patterning, the diffusion distance of the activating agent in the plane direction can be ignored.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for forming a light emitting layer of a thin film type EL element among intrinsic EL elements.

[Prior Art] Although E and L have a long history, they have faced major challenges in terms of brightness and lifespan, and have been in decline. However, in recent years, Bell Laboratories in the United States has announced a thin-film EL device called 1Lumosene, which has the potential for high brightness and multicolor, and Sharp's thin-film EL device with double insulating layers has been released. EL devices are once again attracting attention as they have achieved high brightness and long life.

By the way, in order to manufacture a thin film type EL element, for example, a transparent electrode such as I-tin-O (indium tin oxide) is formed on the surface of a glass substrate, and a first insulating layer such as Y2O3 is formed on the surface of the transparent electrode.

Then, M is applied to the base material made of ZnS phosphor on the surface of the first insulating layer.
After forming an n-doped light-emitting layer and heat-treating it to improve the crystallinity of ZnS, a second insulating layer is coated and an A9 electrode is formed to obtain an EL element.

Here, the ITO film is usually formed by an ion blasting method, and the first and second insulating layers are formed by an electron beam (EB) evaporation method. The method of forming the light emitting layer differs depending on the type of base material and activator. For example, sputtering is generally used for ZnS:TbF3, and EB is used for ZnS:Mn.
The vaporization method is used. This is because the activation form and distribution state of the activator in the light emitting layer are greatly influenced by the film forming conditions and film forming method. Incidentally, when forming a light-emitting layer, it is common to use an evaporation source or target in which a base material and an activator are mixed. But for example ZnS:
In the case of Ln, etc., since the sublimation temperatures of ZnS and ln are different, many 1-n clusters occur, making it difficult to uniformly dope into ZnS. Therefore, a co-evaporation method has also been developed in which the base material and the activator are vapor-deposited from separate evaporation sources.

[Problems to be Solved by the Invention] For example, when forming a light-emitting layer of ZnS:Mn, it can be formed by the same EB evaporation method as the first insulating layer, which is advantageous in terms of process. However, in the case of a light-emitting layer of Nakarazns:TbF3, after forming the first insulating layer by the E8 vaporization method,
The light-emitting layer must be formed by an ion blasting method, which requires a plurality of film forming apparatuses and complicates the process, causing an increase in cost. Zarani Zn
In the case of a multicolor EL element having two types of light emitting layers, S:Mn and ZnS:TbF3, the process becomes even more complicated because the methods for forming the respective light emitting layers are different.

The present invention was made in view of these circumstances, and
The purpose is to simplify the process.

[Means and effects for solving the problem] The present inventors have reexamined the manufacturing process of thin film EL elements. And Z
We focused on a heat treatment step that is performed to improve the crystallinity of ZnS after forming a light emitting layer using nS as a base material. That is, this heat treatment is usually performed by heating at 600 to 650'C for 1 to 2 hours, and it was recalled that the activator is doped into the base material by diffusion using this heat. As a result of extensive research, the present invention was completed by discovering that the activator is easily and uniformly doped into the base material under the above conditions.

That is, the method for forming a light-emitting layer of a thin film EL element of the present invention that solves the above problems includes a first step of forming a first thin film, which serves as a base material of a fluorescent semiconductor material, on the surface of a substrate, and a step of forming a first thin film on the surface of the first thin film. a second step of forming a second thin film made of an activator; and a third step of diffusing the activator from the second thin film into the first thin film by heating.
It is characterized by process and more.

The first step is a step of forming a first thin film that becomes a base material of the fluorescent semiconductor material. As this base material, ZnS, a mixed crystal of 7nS and CdS, etc., which have been conventionally used as a base material, are used. Further, as the substrate, a transparent substrate such as a glass substrate having a transparent electrode on its surface, or a transparent substrate having an insulating layer on its surface can be used. To form this first thin film, sputtering method, vacuum evaporation method, EB
Known film forming methods such as vapor deposition and MOCVD can be used.

In the second step, a second thin film made of an activator is formed on the surface of the first thin film. Here, the activator is an impurity that is doped into the base material and becomes a luminescent center, such as Mn, TbF3, Tb
2O3, PrF3, NdF3, SmF3, EuF3
, DVF3, HOF3, ErF3, TmF3, Yb
It can be selected from F3, CrF3, MnF3, etc. and used. Depending on the type of activator, light emission of different colors can be obtained. The film forming method for forming this second thin film is as follows:
Preferably, the same deposition method used to form the thin film is used.

In this second step, a second thin film can be formed from a plurality of types of activators by patterning. Therefore, multi-colored thin film EL elements can be easily formed.

The third step is a step of heating the entire substrate having the first thin film and the second thin film to diffuse and tope the activator of the second thin film into the first thin film, thereby forming a light emitting layer. is. As will be described later, the conditions necessary for the diffusion of the activator include heating in a temperature range of 500 to 700° C. for 1.5 hours or more.

However, considering the effect of heat on the base material, the conventional Z
The heat treatment conditions for improving the crystallinity of the nS base material are 1 to 2 hours at 600 to 650°C, more preferably 1.
Preferably, the mixture is heated for 5 to 2 hours.

Note that in the third step, the activator diffuses not only in the depth direction of the first thin film but also in the surface direction. Therefore, if a plurality of second thin films are formed by patterning, there is a concern that patterning may be disturbed. The diffusion distance of the Shikashi activator is about 600 nm at most, which is sufficient, so even if the patterning width is Q, 3 mm, the diffusion distance in the plane direction is about 0.3% of the width and can be almost ignored. Good too.

After forming the light emitting layer, a second insulating layer is formed using Y203 or the like, and finally a back electrode is formed to obtain a thin film type El element.

[Effects of the Invention] According to the method for forming a light emitting layer of a thin film EL element of the present invention,
A first thin film made of the base material is formed in the first step, and a second thin film made of the activator is formed in the second step. Therefore 2
Unlike conventional methods in which films are formed from different materials at the same time, there is no need to pay attention to the activation form or distribution state of the activator during film formation, and the film formation method can be selected. In other words, since the first thin film and the second thin film can be deposited using a deposition method that forms an insulating layer, only one film deposition device is required and the number of man-hours is reduced, improving productivity and significantly reducing costs. I can try something.

[Example] Hereinafter, the present invention will be specifically explained using examples. In this example, a two-color thin film type EL element shown in FIG. 1 is manufactured. This EL element includes a glass substrate 1, a transparent electrode 2 formed on the surface of the glass substrate 1, a first insulating layer 3 formed on the surface of the transparent electrode 2, and a first insulating layer 3 formed on the surface of the first insulating layer 3. The light emitting layer 50 and the second light emitting layer 60, the second insulating layer 7 formed on the surfaces of the first light emitting layer 50 and the second light emitting layer 60, and the second insulating layer 7
It is composed of a back electrode 8 formed on the surface.

A transparent electrode 2 made of a JTO film was formed on the surface of the glass substrate 1 by an ion blating method using an EB heating evaporation source. Furthermore, a first insulating layer 3 made of Y2O3 was formed on the surface of the TO film by EB evaporation. Table 1 shows the respective film forming conditions.

(First step) On the surface of the first insulating layer 3 of the substrate according to the present invention obtained above, the first thin film 4 shown in FIG. 2 was formed from 7 nS by EB evaporation method. The film thickness was 600 nm, and the film forming conditions are shown in Table 1.

(Second Step) Next, the surface of the first thin film 4 was patterned, and the second thin film 5 shown in FIG. 3 was formed from Mn by EB evaporation.

In order to make the light-emitting layer using Mn as an activator contain 0.5% by weight of Mn, the film was formed to have a thickness of about 2 nm, taking into consideration the density of each material.

Thereafter, rough patterning is applied to the surface of the first thin film 4 on which the second thin film 5 is not formed.
A second thin film 6 shown in FIGS. 3 to 4 was formed. Here Tb
In order to make the light-emitting layer containing F3 as an activator contain 3% by weight of F3, the film was formed to have a thickness of about 1 Qnm in consideration of the density of each material. Table 1 shows the respective film forming conditions.

(Third step) Next, the Mn in the second thin film 5.6 is heated as a whole.
and TbF3 are each diffused into the first thin film 4.

Here, in order to set the heat treatment conditions, as a preliminary experiment, when the heat treatment temperature was varied, the treatment time and Mn and Tb
The relationship between the depth of diffusion of F3 into ZnS was investigated. The results are shown in Figures 5 and 6 (shown here).
It was carried out in a vacuum of 4×10 −3 pa, and the diffusion depth was determined by Auger analysis.

From FIGS. 5 and 6, when the heat treatment temperature is below 400° C., the diffusion depth reaches a plateau at a shallow position. Therefore, it can be seen that a temperature of 500'C or higher is desirable. However, if the temperature exceeds 800'C, the glass substrate 1 will become soft, so a temperature in the range of 500 to 700'C is preferable.This range includes 600 to 650'C, which is the conventional heat treatment temperature. 600-6 if you take into account the effect of heat on
A range of 50'C is particularly desirable.

Therefore, in this example, heat treatment was performed at 600'C for 1.5 hours in a vacuum of 2 to 4 x 10-3 Pa to form a second thin film of 5.6
The Mn and DbF3 inside are diffused into the first thin film 4, and the first light emitting layer 50 made of ZnS:Mn and the Zn
A second light emitting layer 60 made of S:TbF3 was formed. 1st
The film thicknesses of the light-emitting layer 50 and the second light-emitting layer 60 were approximately the same.

(Formation of EL element) Then, on the surfaces of the first light emitting layer 50 and the second light emitting layer 60,
The second insulating layer 7 was formed from Y2O3 by EB evaporation under the same conditions as the first insulating layer 3. Furthermore, a back electrode 8 was formed from the A layer on the surface of the second insulating layer 7 by EB evaporation to obtain the two-color thin film type EL element shown in FIG. The film forming conditions are shown in Table 1.

The obtained two-color EL device clearly emitted light in two colors of green and yellow-orange upon application of an alternating current voltage.

In other words, according to the method for forming the light emitting layer of this example, since the EB evaporation method is used in all steps from the formation of the first insulating layer 3 to the formation of the back electrode 8, only one film forming apparatus is required and the number of man-hours is reduced. Productivity will improve as well.

Therefore, it is possible to significantly reduce costs.

[Brief explanation of drawings]

The drawings relate to one embodiment of the present invention, and FIG. 1 shows a formed two-color thin film type E [cross-sectional view of the device,
This figure and FIG. 4 are sectional views showing a state in the middle of forming the EL element of FIG. 1, respectively. Figures 5 and 6
The figure is a graph showing the relationship between heat treatment time and diffusion depth. 1... Glass substrate 2... Transparent electrode 3...
-First insulating layer 4...First thin film 5...Second
Thin film 6... Second thin film 7... Second insulating layer 8... Back electrode 50... First light emitting layer
60...Second light-emitting layer patent applicant Toyota Motor Corporation agent Patent attorney Mizuo Okawa 1 Figure 2 Figure 4

Claims (1)

[Claims] (1) A first step of forming a first thin film to serve as a base material of the fluorescent semiconductor material on the surface of the substrate; a second step of forming a second thin film made of an activator on the surface of the first thin film; and by heating. A method for forming a light-emitting layer of a thin-film EL device, comprising a third step of diffusing the activator from the second thin film into the first thin film.