JPS6124192A - Thin film electroluminescent 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 (Field of Industrial Application) The present invention relates to a thin film electroluminescent device that exhibits electroluminescence upon application of an alternating current electric field.

(Prior art) Conventionally, AC-operated thin film electroluminescent elements (
In order to improve the brightness and luminous efficiency of thin-film EL devices (hereinafter referred to as thin-film EL devices), and to obtain stable operation over long periods of time,
0.5 to 3 mobs of Mn or Tb as the luminescent center
F3. SmF3. Zn8. to which PrF, etc. were added.
A light-emitting layer such as Zn8e, YtOs;
B, Pb TiO@ + Ba Tl 0g +
A thin film EL element with a so-called double insulation structure, which is sandwiched between two insulating layers such as 81 B N4, was used.

An example of the basic structure of a conventional double insulator thin film 11imL element is shown in FIG.

In FIG. 1, 1 is a glass substrate, 2 is "t OB +
8nO, ITO (Indium Tin Oxide)
) or a transparent electrode on the substrate side made of a metal thin film, etc., and 3 is Y20B, AA20,1, PbTiO deposited thereon by electron beam or sputtering vapor deposition method.
3. BaTi0. , 51 mN4, etc., with Mn, TbF, etc. deposited on top of the insulating layer.

This is a light-emitting layer made of Zn8 containing luminescent centers such as SmFl and PrF. This light-emitting layer 4 is also manufactured by electron beam evaporation, submersible evaporation, or the like. Reference numeral 5 denotes an insulating layer deposited on the light emitting layer 4, and the deposition method and material are the same as those for the insulating layer 43. Reference numeral 6 is an electrode made of B or ITO, which is further deposited thereon, and 7 is an AC power source for driving the EL element, which is connected to the electrodes 2 and 6.

However, such a double insulation structure inevitably increases the operating voltage. Therefore, single-insulated thin film EL elements that operate at a much lower voltage have come into use. Single insulation fiE
An example of the basic structure of an L element is shown in FIG.

In the EL element shown in FIG. 2, the insulating layer 3 is removed. The rest is the same as the EL element shown in FIG.

Next, the light emission principle of the EL element will be explained with respect to the BL element having the structure shown in FIG.

The light emitting layer 4 is considered to be a simple capacitor before the start of light emission. When an AC voltage from a power source 7 is applied between the electrodes 2 and 6, a voltage is applied to the light emitting layer 4 and the insulating layer 5 according to their respective capacitances. When the electric field applied to the light emitting layer 4 is sufficiently high (approximately 106 V/l:m or more), electrons are excited in the conduction band of the light emitting layer 4. These electrons are sufficiently accelerated by the electric field and collide with the luminescent center. As a result, when the electrons in the luminescent center that have risen to an appropriate excited state return to the ground state, light with an energy value unique to the luminescent center is emitted. In reality, the emission spectrum has a certain degree of broadening due to interaction with the crystal lattice and the like. Mn, the luminescent center mentioned earlier
, TbF, , SmF, , PrFB, etc., have emission energy in the visible range, so strong light emission is observed.

(Problems with the Prior Art) In an EL element, it is very important to make the rise of brightness relative to an applied voltage steep when manufacturing a matrix-type or box-type panel. The steeper the voltage, the more the voltage required to turn on or off the pixels of the panel (hereinafter referred to as modulation voltage)
Therefore, the power consumption is reduced, and the uniformity of the luminance when the entire screen is lit is increased, and a large contrast can be obtained with a small modulation voltage. However, in the conventional single-insulator EL element, the emission start voltage of the light emitting layer on the side in contact with the insulating layer is different from the emission start voltage on the side in contact with the electrode such as ITO.

For this reason, the single-insulation type EL element has the disadvantage that the brightness rises slowly with respect to the applied voltage.

(Object of the Invention) An object of the present invention is to eliminate the above-mentioned conventional drawbacks and to provide a single-insulation type thin film electroluminescent device having a sharp rise in luminance. The thin film electroluminescent device of the present invention is a thin film electroluminescent device in which a transparent electrode, a light emitting layer, an insulating layer, and a counter electrode are sequentially laminated on a transparent substrate, and a metal thin film is provided between the light emitting layer and the insulating layer. It is configured with the following features.

The present invention provides a thin metal film between a light-emitting layer and an insulating layer, and by making the interfaces on both sides of the light-emitting layer interfaces with properties similar to those of metal, the brightness rises sharply. Type thin film El,
The device was designed so that the device could be obtained.

There are no particular restrictions on the material of the metal thin film, and any material may be used, but Ti, W, Or, Mo, and M, which have low metal diffusion, can be used.
A high melting point metal such as n is preferable. Further, the thickness of the metal thin film is desirably in the range of several X to several hundred X. The reasons for this are (1) sufficient steepness can be obtained with this film thickness, and (2)
) If the thickness of the film is too thick, current will concentrate through the metal thin film at the dielectric breakdown part of the element, which will increase the size of the breakdown part and reduce the reliability of the element. Things like this can be mentioned.

Note that the metal thin film according to the present invention may be provided only on the light emitting part of the EL element. Therefore, when applying a metal thin film to an EL panel having matrix or box type electrodes, it is sufficient to provide the metal thin film only in the light emitting part where the upper and lower electrodes intersect, thereby eliminating cross-over between multiple pixels. The brightness rises steeply and an L element can be obtained. In addition, 100% of the metal thin film
In the case of a very thin film of A or less, the metal thin film itself has a high resistance, and crosstalk between pixels can be eliminated even if the metal thin film is provided over the entire display element.

(Example) Next, embodiments of the present invention will be described using the drawings.

FIG. 3 is a sectional view of one embodiment of the present invention.

In FIG. 3, 8 is a metal thin film provided between the light emitting layer 4 and the insulating layer 5. Ti was used as the metal thin film, and its thickness was 20A. Further, as the light-emitting layer 4, ZnS doped with Mn as a light-emitting center was used. When the EL element thus prepared was driven with a 200Hz sine wave, its luminance was lcd/n! The voltage required to increase from 100 Cd/♂ to 100 Cd/♂ was reduced from several inches to more than ten inches compared to the conventional single insulation type EL element without the metal thin film 8.

(Effects of the Invention) As is clear from the above explanation, according to the present invention, it is possible to obtain a high-luminance EL element in which the rise in luminance is steeper and the luminance is improved by about 10 degrees compared to the conventional one. I can do it.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional double-insulated thin film BL element;
The figure is a cross-sectional view of a conventional monthly edge type thin film EL element, and FIG. 3 is a cross-sectional view of an embodiment of the present invention. 1...Glass substrate, 2...Transparent electrode,
3...Insulating layer, 4...Light emitting layer, 5...
...Insulating layer, 6...Electrode, 7...
- AC power supply, 8... Metal thin film. 721. ＼ Agent Patent Attorney Fu Uchihara ″, −/′ −

Claims (1)

[Claims] A thin film electroluminescent device comprising a transparent electrode, a light emitting layer, an insulating layer and a counter electrode successively laminated on a transparent substrate, characterized in that a metal thin film is provided between the light emitting layer and the insulating layer. Luminescence element.