JPS59154793A - 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] The present invention relates to a thin film EL device.

A thin film EL element emits light by applying a voltage to an optically active light emitting layer such as a ZnS:Mn thin film.

A characteristic of the thin film EL element is that it emits light from a surface of a transparent thin film and has excellent visibility. In addition, it is an all-solid-state device manufactured using a thin film process, and as a display panel, it is lightweight, extremely thin, and resistant to mechanical shock, and it can easily achieve high resolution using photoringraph technology. In addition, the luminance is high, and the luminance rises rapidly with respect to the applied voltage at a threshold voltage or higher, so it is excellent in time-division drivability as a display panel. Because of these features, thin film EL panels have attracted attention as dot matrix type flat displays and are expected to be used as display devices for information terminals and the like.

There are two types of thin-film EL devices: a DC type in which electrodes are formed on both sides of a light emitting layer and emits light using a direct current voltage, and an AC type in which an electrical insulating layer is provided between the light emitting layer and the electrode and light is emitted by an alternating voltage. At present, the AC type is superior in light emission brightness and reliability, although the light emission voltage is high.

FIG. 1 is a sectional view of an example of a conventional AC type EL element.

This EL element is an AC type EL element called double insulation type. Indium tin oxide (hereinafter referred to as I) was deposited on a transparent glass substrate.
Transparent electrode 2゜Y20R* Ta205 such as TO)
* First insulating layer 3° such as S ia N4 or ZnS
Mr? A light emitting layer activated with ions or rare earth fluorides such as TbFs, etc. A second insulating layer made of the same material as the first insulating layer or a different insulating layer.
Insulating layer 5. The basic structure consists of a back electrode 6 and a transparent box 7
(Electroluminescence can be caused by applying an alternating voltage between the electrode and the back electrode.

In such an EL element, it is important to improve the basic characteristics of brightness and drive at a low voltage. In order to improve these characteristics, optimization of constituent materials, film formation and heat treatment processes, and optimization of the film thickness of each layer are being considered. For example, forming an insulating layer or employing a high dielectric insulating layer such as PbT10s results in an increase in the effective voltage applied to the emissive layer.
The external voltage required for light emission can be reduced. However, in the former case, the EL element is easily destroyed, resulting in a lack of reliability over its lifetime, and in the latter case, there is also difficulty in reproducibility of the film formation, and the capacitance t1 of the EL element increases, resulting in a high speed. It has disadvantages such as not being suitable for driving.

Regarding the light-emitting layer-1, it is known that Zn5e starts emitting light at a lower voltage than ZnS depending on the band gap, but it has a drawback of low saturation luminance. Furthermore, regarding the luminescent center, Mn, which is currently widely used,
No properties exceeding 2+ have been obtained.

As described above, it is very difficult to lower the driving voltage without sacrificing the luminance and reliability.At present, a driving voltage of about 150 to 200 cm is required.

Such a high operating 1E pressure has the disadvantage of being a major obstacle to the implementation of an IC drive circuit, which is essential for a display device.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks, to provide a thin film EL element that can be driven at a low voltage and has high brightness.

According to the present invention, there is provided a transparent substrate, a transparent electrode provided on the entire surface of the transparent substrate, a back electrode provided opposite to the transparent electrode, and a space between the transparent electrode and the back electrode. A thin film EL device is obtained, which includes a light emitting layer and an insulating layer, and an interface layer of an amorphous semiconductor provided between the light emitting layer and the insulating film.

The amorphous semiconductor is amorphous Sl or amorphous %Six
C1-x is used.

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

FIG. 2 is a sectional view of one embodiment of the present invention.

A TO vaporized film with a thickness of 0.02 μm is provided as a transparent electrode 2 on a transparent glass substrate 1, and a Si3N4 film of 0.2 μm is deposited thereon as a first insulating layer 3 by reactive sputtering.
It is formed to a thickness of 5 μm. A first interface layer 7 is provided by sputtering. This will be discussed later. ZnS:M containing 0.5 mol% Mn as a light-emitting layer 4 on the first interface layer 7
Neo, formed to a thickness of 6 μm. A second interface layer 8'f is provided on this. This will also be discussed later. Second
Si3N4 is deposited on the interface layer 8 as the second insulating film 5.
This is deposited to a thickness of 25 μm, and the back electrode 6 is formed thereon using an At deposited film.

The aforementioned first and second interfacial layers 7 and 8 were prepared using two types of materials, namely (1) amorphous S1 of about 6O
Trial made by sputtering to thickness A, (2) Amorphous 5i
There are two types of specimens made with snow ivy to a thickness of about 150A. In particular, EL with amorphous Si as an interface layer
In the device, the insulating layer also targeted Si, and the film was continuously formed by switching the sputtering gas kN2-Ar mixed gas and Ar-H2 mixed gas without taking it out from the ivy chamber.

FIG. 3 is a characteristic curve diagram showing the relationship between applied voltage and luminance of one embodiment shown in the second example.

In the figure, A is a conventional EL transducer without the above-mentioned interface layer.
B and C are amorphous S as the first and second interfacial layers, respectively.
This is an EL crystal using i and amorphous sic-. Luminance measurements were performed using a 5 kHz sine wave. As is clear from Fig. 3, EL elements B and C provided with an interface layer can achieve luminance equal to or higher than that of the conventional EL element A, even when the applied voltage is lower than that of the conventional EL element A without an interface layer. It will be done. By providing the interfacial corner metal in this way, it is possible to lower the driving voltage and improve the brightness.

In the above embodiment, the interface layer was provided on both sides of the entire light emitting layer, but it may be provided only on one side. Particularly when it is provided on the back side, there are advantages of reducing loss due to light absorption and of avoiding the adverse effects of diffusion caused by heat treatment of the light emitting layer. Further, although the above embodiment has been explained using a double insulation type EL element, it goes without saying that the present invention can also be applied to a single side insulation type EL element.

The principle of electroluminescence in ZnS:Mn, etc. is considered as follows. A high electric field applied to the light-emitting layer accelerates conduction electrons and turns them into thermoelectrons. Thermionic electrons that have obtained sufficient energy (2.2 eV or more for Mn excitation) collide with the luminescent center and directly excite the valence electrons of the luminescent center from the ground state to the excited state. Light emission occurs when the excited state returns to the ground state.

In addition to such an excitation process, the process of creating conduction electrons, which is the origin of thermoelectrons, is particularly important in AC type EL elements. A
The C-type EL crystal is surrounded by an insulating layer and cannot accept surface electron gold from the outside of p1.Therefore, conduction electrons are electrons trapped in the interface level formed at the interface with the insulating layer or shallow electrons inside the phosphor. It is thought that the trap is injected into the conduction band by a tunnel effect due to a high electric field. It is believed that the interfacial layer of the present invention contributes to supplying a large amount of conduction electrons to the light emitting layer at a low electric field. That is, the interface layer of the amorphous semiconductor forms a large amount of interface levels at the interface and plane between the interface layer and the light-emitting layer, and between the interface layer and the insulating layer, and the amorphous a-semiconductor has many trap levels. It is thought that a large amount of electrons captured in these levels are injected into the light emitting layer in multiple directions by applying a very low external voltage, resulting in lower voltage and higher brightness of the thin film EL element.

The interfacial layer of the present invention can be easily formed into a film, and from the viewpoint of stability and transparency, amorphous Si and amorphous 5ixCt-
x (0,1(x (1)) is desirable.These materials are not transparent, but as an interfacial layer, the
Since the effect is exhibited at a film thickness of 00A or less, the effect of improving light absorption is more than that of gold, and the effectiveness is not impaired.

As explained in detail above, according to the present invention, it is possible to obtain a thin film EL element that can reduce the driving voltage and increase the surface brightness.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an example of a conventional AC type EL element, Fig. 2 is a cross-sectional view of an embodiment of the present invention, and Fig. 3 is the relationship between applied voltage and luminance of the actual M example shown in Fig. 2. FIG. l...Transparent glass substrate, 2...Transparent electrical contact, 3...First breakdown, island, 4...Light emitting layer, 5... . . . second insulating layer, 6 . . . back side'
i1\pole, 7...first interface layer, 8...
Second interfacial layer. Figure 1 Figure 7 Figure 3m

Claims (2)

[Claims] (1) a transparent substrate, a transparent electrode provided on the entire surface of the transparent substrate, a back electrode provided opposite to the transparent electrode, and a light emitting layer provided between the transparent electrode and the back electrode; A thin film EL device comprising an insulating layer and an amorphous semiconductor interface layer provided between the light emitting layer and the insulating film. (2) The thin film EL device according to claim (1), in which amorphous Si or amorphous SiC-X is used as the amorphous semiconductor.