JPS61273894A - Thin film el element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a thin film EL device that emits EL (electroluminescence) light in response to the application of an electric field, and particularly relates to a thin film EL device doped with a compound of a rare earth element as a light emitting center of a light emitting layer. Related to devices 0 <Prior art and its problems> In a thin-film EL device in which a light-emitting layer that emits EL light upon application of an alternating current electric field is covered with a dielectric layer, the light-emitting layer is made of ZnS, etc.
- When constructed from a material in which a group compound is doped with a rare earth fluoride, etc. - EL elements that emit light of various colors can be obtained depending on the type of rare earth element.

For example, TbFa, SmF3. TmF3 or PrF3
When using rare earth fluorides such as, green and red respectively.

A device that emits blue and white light can be obtained. When a rare earth element alone or another rare earth compound is used, the same luminescent color can be obtained, but the luminance and luminous efficiency are lower than when a rare earth fluoride is used. In addition, for elements like Eu that can be divalent or trivalent, it is possible to control the valence, such as when doped in the form of fluoride (EuFa), it can be doped relatively easily while remaining trivalent. Therefore, when doping a light-emitting layer with a rare earth element as a luminescent center, it is often used in the form of a fluoride.

To produce a light-emitting layer in which rare earth fluoride is the main luminescent layer, a film is formed by electron beam evaporation using sintered pellets made of ZnS mixed with an appropriate amount of rare earth fluoride in advance, or a film is formed using rare earth fluoride powder and ZnS. A method of forming a film by RF (reactive) sputtering or the like using Kasuri powder mixed with the powder of 12. It will be done. The light-emitting layer produced by these methods can be used as a light-emitting laser.
The central rare earth fluoride is usually contained in the ZnS crystal in the form of molecules of RE-Fa.
Atomic ratio (F) of rare earth atoms (RE) and fluorine atoms (F)
/RE) is 3 or very close to 3. However, when rare earth fluoride, which is a relatively large molecule, enters the ZnS crystal, it deteriorates the crystallinity of the surrounding area.
This results in a decrease in luminance and luminous efficiency. Here, if rare earth atoms (RE) can be replaced with zinc atoms (Zn), deterioration of the crystallinity of ZnS can be suppressed to a small level. However, rare earth atoms are usually trivalent (RE
3+ ), and zinc is divalent (Zn''), so RE3+ is '1, and when Zn 2+ is replaced, there will be an excess of positive charge of +1. One valent fluorine (F-1) at an interstitial position is sufficient.

゛ Therefore, if all rare earth atoms are ideally substituted with zinc, the ratio of rare earth atoms to fluorine atoms (F/RE) in the light emitting layer will be 1.

<Summary of the Invention> In view of the above-mentioned problems, the present invention is based on a rare earth atom (RE) and a fluorine atom (F) of a rare earth fluoride doped as a luminescent center (active substance) into a luminescent layer base material such as ZnS. By setting the atomic ratio (F/RE) in the range of 0.5 to 2.517), distortions and defects in the crystal lattice caused by doping with rare earth fluorides are suppressed to ensure luminance brightness and luminous efficiency. The object of the present invention is to provide a thin film EL device that has a high-performance thin-film EL device.

<Embodiment> FIG. 1 is a basic configuration diagram of a thin film EL element for explaining one embodiment of the present invention.

After cleaning the surface of a transparent substrate such as a glass substrate 1, transparent electrodes 2 made of an ITO film or the like are formed into strips and arranged in parallel to the clean surface of the glass substrate 1.

On top of this is Si02. as the lower dielectric layer 3. YzOaI
Si3N4 or the like is deposited to a thickness of about 100 OA to 300 OA by a thin film forming technique such as sputtering or electron beam evaporation. Next, ZnS:TbFx is formed as a light emitting layer 4 on top of this.
The deposition source is a sintered pellet in which ZnS is doped with a predetermined amount of terbium fluoride represented by TbFx (x = 1 to 3) as an active material that serves as a luminescence center, and this is deposited using an electron beam evaporation port. Form a film. In addition to electron beam evaporation, the film may be formed by RF sputtering using a mixture of ZnS powder and TbFx powder as a target. Further, as the upper dielectric layer 5, 5i02. AJ203
．． A light emitting layer 4 is buried in the upper and lower dielectric layers 3 and 5 by coating Y2O3°Si3N4 or the like in a single layer or a composite film.

The upper dielectric layer 5 is formed in the same manner as the lower dielectric layer, and its thickness is approximately +00 OA to 500 OA. On the upper dielectric layer 5, strip-shaped strips A2 are arranged as back electrodes 6 in parallel in a direction orthogonal to the transparent electrode 2. A matrix electrode structure is formed by the transparent electrode 2 and the back electrode 6, and a matrix-like light emitting display is performed.

When an alternating current electric field is applied between the transparent electrode 2 and the back electrode 6, this alternating electric field is induced in the light emitting layer 4, and carriers are attracted as hot carriers from the base material of the light emitting layer 4 to the interface of the light emitting layer 4 corresponding to the electric field polarity. to form an internal charge. Next, when the electric field polarity is reversed, this internal charge is superimposed on the induced electric field, and the hot carriers are swept to the other interface of the light emitting layer 4.

In this process, Tb electrons of TbFx doped as a luminescent center are excited by collision, and an electromagnetic spectrum is emitted from Tb. This electromagnetic spectrum is observed as green EL emission through the glass substrate 1. In order to maintain high luminance and luminous efficiency, it is necessary to improve the crystallinity of the ZnS crystal grains that are the base material of the luminescent layer 4 so as not to inhibit the activity of hot carriers. The Tb atom of TbFx doped as a center is efficiently replaced with a Zn atom. Tb is 3
Since Zn is divalent, when Tb is placed at the position of Zn, an excess positive charge of +1 is generated.

This is compensated for by F atoms.

FIG. 2 shows the relationship between the ratio of Tb and F (F/Tb) in the light emitting layer 4 and the luminance. The ratio of Tb to F in the light emitting layer 4 is 1□ compared to ZnS in the sintered pellet during electron beam evaporation or the target during sputtering.

, i is determined by adjusting the composition of Tb and F to be sputtered or by controlling the deposition conditions or sputtering conditions. The horizontal axis represents F/Tb ratio, and the vertical axis represents luminance. As is clear from the figure, the luminance is high when SF/Tb is in the range of 0.5 to 2.5, and is particularly high in the range of 1.0 to 2.01'.

2(i,. Therefore, TbFx:, M doped in the light emitting layer 4 is TbF
1, where F/Tb falls within the above range instead of the shape of 3.

The light emitting layer 4 is formed as shown in FIG.

3. Although the above embodiment describes the case where TbFx is used as the luminescent center, the present invention is not limited to this, and can also be applied to cases where other rare earth fluorides are used. It is possible.

<Effects of the Invention> As detailed above, according to the present invention, when a rare earth fluoride is doped into the luminescent layer as a luminescent center,
high-quality thin film i' without reducing luminance when
Et, the element can be constructed.

Go]

[Brief explanation of the drawing]

fj, ji7,, FIG. 1 is a thin film description of one embodiment of the present invention. FIG. 2 is a characteristic diagram showing the relationship between F/Tb and luminance of TbFx doped into a light emitting layer. 1...Glass substrate 2...Transparent electrode 3...
Lower dielectric layer 4... Light emitting layer 5... Upper dielectric layer 6... Back electrode

Claims (1)

[Claims] 1. In a thin film EL device in which a rare earth fluoride is doped as a luminescent center in a light emitting layer base material, the atomic ratio of rare earth atoms (RE) and fluorine atoms (F) in the light emitting layer (F/
A thin film EL device characterized in that RE) is in the range of 0.5 to 2.5.