JPH01100892A - Thin film EL element - Google Patents

Abstract

PURPOSE:To make it possible to obtain a high brightness with a low driving voltage by adding one or more elements of Sc, Y, La, Li, Na, K, Pb, Cs, Mo, Co, Cr, and Gd as the doping material. CONSTITUTION:On a transparent substrate 1 such as a glass substrate, a trans parent electrode 2 of ITO or the like is laminated. Then the first insulating membrane 3 consisting of Ta2O5 or the like is laminated 0.6mum in the spattering. After that, a luminous layer 4 using ZnS as the basic material, Mn as the lumi nous center, and one or more elements of Sc, Y, La, Li, Na, K, Pb, Cs, Mo, Co, Cr, and Gd as the doping material is laminated 0.35mum in the MSD method.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a dopant added to a light-emitting layer of a thin film EL element that can achieve high brightness with low voltage driving.

(Prior Art) Thin-film EL elements have high brightness and are composed of thin films, so they are promising candidates as display elements that can be applied to next-generation flat display panels.

The double insulating film structure of a conventional thin film EL element is shown in Figure 4.
On a transparent substrate 1, a transparent electrode 2 made of ITO or the like, and a T
The first insulating film 3 made of a t Os or the like and the base material (Z
A light-emitting layer 7 consisting of a luminescent center substance (Mn, etc.) and a luminescent center substance (Mn, etc.)
, a second insulating film 5 made of T az Os or the like, and a metal electrode 6 are sequentially laminated.

Next, a light emitting mechanism of a thin film insulating film element having a double insulating film structure will be explained.

Transparent electrode 2 and metal electrode 6 of the thin film EL element explained above
When an alternating current electric field is applied to the light emitting layer 7 through the first insulating film 3 and the second insulating film 5, the electric field is applied to the light emitting layer 7. Then, due to the electric field, electrons in the valence band existing in the base material receive energy and become present in large numbers in the conduction band (
electronic avalanche phenomenon).

When this electron avalanche phenomenon occurs, the number of 4-transfer electron tubes increases and a large number of luminescent center substances are brought into an excited state.

When the electrons in the excited state return to the ground state, the energy is converted into light and released, causing the thin film EL element to emit light.

(Problems to be Solved by the Invention) Conventional thin film EL devices use electrons in the valence band existing in the base material as the moving charges, but the amount of moving charges is not sufficient, and therefore thin film EL devices In order to emit light, a high driving voltage is required, and even though a high voltage is applied,
I couldn't get high brightness.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a structure capable of obtaining a thin film EL element driven at a low voltage and having high brightness.

(Means and effects for solving the problems) In order to solve the above problems, the present invention uses Sc,
YS La, Lt, NaK, Pb, Cs, Mo, C0
One or more types of elements among 1Cr and Gd are added to the light emitting layer.

When an electric field is applied to the thin film EL element, the valence electrons of the dopant added to the light emitting layer become mobile charges and collide with the ground state electrons of the luminescent center substance to excite them. Compared to conventional methods that use only valence electrons that exist in the base material, by adding a dopant, the amount of mobile charges increases and more electrons collide with the ground state electrons of the luminescent center substance. .

Therefore, the number of excited-state electrons increases and the amount of light emission increases.

(Example) The thin film EL device of the present invention will be described below with reference to the drawings.

An example will be explained in which ZnS is used as the base material, Mn is used as the luminescent center substance, and Sc and K are used as the dopant materials. FIG. 1 shows a cross-sectional view of an embodiment of the thin film EL element of the present invention.

On a transparent substrate 1 such as a glass substrate, a transparent electrode 2 made of ITO or the like is laminated, and a first tPA film 3 made of zero-order T az OS or the like is laminated by a 0.6 μm sub-lid method. Then, ZnS is used as the base material, Mn is used as the luminescent center,
The light emitting layer 4 made of Sc and K as dopants is MSD
A thickness of 0635 μm is laminated using the method.

Here, a stacking method using the MSD method will be explained.

FIG. 2 shows a schematic diagram of the MSD apparatus. In a vacuum chamber 11, there are a crucible 12 into which a raw material is placed and a substrate 13. The temperature of the crucible 12 is independently controlled and the raw material is evaporated onto the substrate 13. The inside of the vacuum chamber 11 is evacuated by a vacuum pump 14. In the case of this embodiment, the crucible 12 is filled with Zn, S,
Mn.

Add K and Sc, control the temperature, and add Mn, K, and S.
A ZnS thin film containing c is deposited. Nito Sc shall be 10mo 1% or less with respect to the base material.

By the way, since K and Sc are monovalent and trivalent ions, respectively, they are replaced with the divalent ions of Zn, and their electric charges are compensated.

Next, T a! A second insulating film made of Os or the like is deposited to a thickness of 0.6 μm by sputtering. Finally, metal electrodes made of Af or the like are laminated and wired.

Since the thin film EL device described above contains a dopant in the light emitting layer 4, it emits light at a low voltage even at a low voltage because a large number of mobile charges are generated from the dopant. In addition, since the amount of moving charges is large, many electrons in the ground state of the luminescent center collide with each other, resulting in improved brightness.

FIG. 3 shows the relationship between voltage and luminance of the thin film EL device of the present invention and the conventional thin film EL device.

The thin-film EL element shown in the figure has a driving voltage of 15OV and a saturation luminance of 1700 c d/cm3.
0V, the saturated luminance was 2200 Cd/c+a'', and a thin film EL element with low voltage drive and high luminance could be obtained.

In this example, a case where ZnS is used as the base material, Mn is used as the luminescent center substance, and K and Sc are used as the doping materials is explained, but the combination is not limited to this, and the base material may be SrS or CaS, M as the central substance
It may also be n, Tb, Ce, or Eu. Sc as a dope material
, Y, La, Li, Na, K,
Rh, Cs,, M, o.

One or more elements from among Co, Cr, and Gd may be used.

(Achievements of the Invention) As described above, in the present invention, by adding a dopant to the light-emitting layer, it is possible to lower the electric field value in which mobile charges are generated, and further increase the number of mobile charges at the same electric field value as in the conventional method. Therefore, there is an excellent effect that high brightness can be obtained with a low driving voltage.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the thin film EL device of the present invention, FIG. 2 is a schematic diagram of an MSD method apparatus for laminating the light emitting layers of the thin film EL device of the present invention, and FIG. 3 is the relationship between voltage and luminance of the present invention and the conventional example. This is a graph showing a comparison. FIG. 4 is a cross-sectional view of a conventional thin film EL element. l...Transparent substrate 2...Transparent electrode 3...
First insulating film 4...Emissive layer containing dope material 5...Second insulating film 6...Metal electrode 7...Emissive layer Patent applicant Komatsu Ltd. representative (patent attorney) Oka 1) Kazuyoshi Figure 1 Figure 2 Voltage (Vσ-p) Figure 3 Figure 4

Claims (1)

[Claims] Thin film EL element with double insulating film structure, made of ZnS, SrS,
In a thin film EL device consisting of a base material such as CaS and a luminescent center substance such as Mn, Tb, Ce, Eu, Sm, etc., doping materials such as Sc, Y, La, Li, Na, K, Pb, Cs,
A thin film EL device characterized by adding one or more of Mo, Co, Cr, and Gd.