JPH03141587A - Electroluminescent element - Google Patents

Abstract

PURPOSE:To offer an electroluminescent element whose emission luminance can be controlled by providing a carrier injection means for injecting carriers into a carrier supply layer laminated on a light emitting layer. CONSTITUTION:A carrier supply layer 10 provided between a first insulative layer 3 and a light-emitting layer 4 has a carrier introducing portion 10a which projects from a region where the light-emitting layer 4 is formed. The carrier introducing portion 10a is covered with a thin insulative layer 5a continued to a second insulative layer 5, and a carrier injection electrode 20 serving as a carrier injection means is provided on the thin insulative layer 5a. To actuate such an electroluminescent element, carriers coming from the carrier injection electrode 20 are injected into the carrier supply layer 10 from the carrier introducing portion 10a via the thin insulative layer 5a and the total amount of carriers contained in the carrier supply layer 10 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an electroluminescent device.

[Conventional technology]

The basic structure of a conventionally used electroluminescent element (hereinafter referred to as "rEL element") is shown in FIG. I TO (I
A transparent conductive film 2 such as a ndium-tin-oxide film is formed, and a first insulator M3 is formed on the transparent conductive film 2. Then, a light emitting layer 4 made of ZnS or the like and a second insulating layer 5 are sequentially laminated on the first insulating layer N3. The light emitting layer 4 is sandwiched between the second insulating layers 35.

On the second insulating layer 3, a back electrode 6 made of 8ρ or the like is formed, and a high frequency power source 7 is connected between the back electrode 6 and the transparent conductive film 2. The first insulating layer 3 is made of Si, for example.
It is composed of a film with a laminated structure in which an O□ film and a Si3N4 film are stacked, and the second absolute μN5 is a Si s N
4 membrane and Al1. It is composed of a laminated structure film with O, a film, etc.

When a high frequency voltage from a high frequency voltage source a7 is applied between the transparent conductive film 2 and the back electrode 6, carriers etc. trapped between the light emitting layer 4 and the insulating layer 3.5 become the light emitting center of the light emitting layer 4. The collision excites this luminescent center. Light is then emitted when this luminescent center transitions to the ground state.

This light is transmitted through the glass substrate 1 and observed, and a display is performed in this manner.

However, in such an EL element, the carriers that contribute to light emission are carriers trapped between the light emitting layer 4 and the insulating layer 3.5, and a very small amount of carriers causes collision and excitation of the light emission center. Therefore, there were problems in that the luminous efficiency was poor and the brightness was low.

In order to solve this problem, the inventors of the present invention have proposed an EL element shown in FIG. In FIG. 3, parts corresponding to those shown in FIG. 2 described above are designated by the same reference numerals. In the EL element of this proposed example, carrier supply layers 10 and 11 are provided between the first insulating layer N3 and the light emitting layer 4 and between the light emitting layer 4 and the second insulating layer 5, respectively. This carrier supply! For example, 10.11 is
It is made of a metal such as aluminum, a semiconductor such as sulfur-doped boron nitride, or a transparent conductive film such as ITO.

According to such a configuration, by applying a high frequency voltage from the high frequency power source 7, abundant carriers in the carrier supply layer 1O111 are injected into the light emitting layer 4, and the injected carriers collide and excite the light emitting center. Therefore, the number of collisions between the carrier and the luminescent center increases, improving the luminous efficiency and making it possible to emit light with high brightness. If either one of the carrier supply layers 1011 is provided, the light emitting layer 4
It is possible to improve luminous efficiency and brightness by supplying carriers to.

[Problems to be Solved by the Invention] However, in the configuration of this proposed example, the total amount of carriers in the carrier supply layer 10.11 is maintained at the state at the time of manufacturing the EL element, and this total amount of carriers cannot be controlled. For this reason, it is not always possible to obtain the total amount of carriers that maximizes luminous efficiency and luminance, and it is not possible to control luminance. Therefore, the display quality of the display device could not be improved.

An object of the present invention is to provide an electroluminescent element that solves the above-mentioned technical problems and allows control of luminance.

[Means to solve the problem]

The electroluminescent device of the present invention is characterized in that it is provided with carrier injection means for injecting carriers into the carrier supply layer laminated on the light emitting layer.

[Effect]

According to the configuration of the present invention, the carrier injection means injects carriers into the carrier supply layer in which carriers are injected into the light emitting layer and are accumulated to collide and excite the luminescence center, so that carriers are not accumulated in the carrier supply layer. It becomes possible to control the total amount of carriers.

〔Example〕

FIG. 1 is a sectional view showing the basic structure of an electroluminescent device (hereinafter referred to as "rEL device") according to an embodiment of the present invention. In FIG. 1, parts corresponding to those shown in FIG. 3 described above are given the same reference numerals. In the EL device of this example, the carrier supply layer 10 provided between the first insulating layer 3 and the light emitting layer 4 is
It has a carrier introduction part 10a that protrudes from the formation area. This carrier introduction portion 10a is covered with a thin insulating layer 5a continuous with the second insulating layer 5, and a carrier injection electrode 20 serving as carrier injection means is provided on this thin insulating layer 5a. The ugly insulating layer 5a is
For example, the 2nd M! ! , the edge layer 5 is Si0g film on Si0g film.
In the case of a two-layer structure in which 3N agl is laminated, only a 5iOz film is formed on the carrier introduction part 10a.In starting such an EL element, the carrier injection electrode is 20 to thin insulating layer 5
from the carrier introduction section 10a via the carrier supply layer l
Carriers are injected into O, and the total amount of carriers in this carrier supply layer 10 is controlled. Injection of carriers is achieved by tunnel injection or hot electron injection, for example, by applying a voltage to the carrier injection electrode 20. In this case, the total amount of carriers accumulated in the carrier supply layer 10 can be controlled by controlling the applied voltage and voltage application time.

After injecting carriers in this way, the transparent conductive film 2
By applying a high frequency voltage from the high frequency power source 7 between the back electrode 6 and the carrier supply layer 10.11, carriers from the carrier supply layer 10.11 are injected into the light emitting layer 4, and the light emitting center is excited, thereby emitting light. is emitted. In this case, if the total amount of carriers that collide with and excite the luminescent center is set so that the luminous efficiency is maximized, the luminous efficiency can be further improved than in the above-mentioned proposed example. Furthermore, by controlling the total amount of accumulated carriers, the number of collisions between the luminescent center and the carriers in the luminescent layer 4 is controlled.
Emission brightness can be controlled.

As a result of being able to control the luminance of emitted light in this way, for example, in a display device to which the EL element of this embodiment is applied, it is possible to easily adapt to the usage environment (illuminance, etc.) and set the optimum light source that is most easily visible to the naked eye. It becomes possible to set the brightness, and therefore it is possible to contribute to improving the display quality of the display device.

In this embodiment, carriers are injected from the carrier injection electrode 20 every time the EL element is activated. is the first. This is because the carriers can jump over the second insulating layer 3.5, thereby reducing the total amount of carriers, and the carrier injection performed at the time of starting up the device can reliably bring the luminance to a desired state.

In the above embodiment, carriers were injected into the carrier supply layer 10 between the first insulating layer 3 and the light emitting layer 4.
A carrier injection means may be provided in the carrier supply layer 11 between the light emitting layer 4 and the second insulating layer 5 to inject carriers, and carriers may be injected into both the carrier supply layers 10 and 11. You can do it like this.

Furthermore, when carriers are injected into the carrier supply layer 11 of the six back electrodes, for example (a) by increasing the thickness of a part of the carrier supply layer 11, the second
A part of the insulating layer 5 is made thinner, and carriers are injected from this part.

0)) The second insulating layer 5 is formed to have a relatively thin film thickness, and carriers are injected by applying a higher voltage to the back electrode 6 than the voltage during light emission driving.

By using technical means such as the following, the back electrode 6 may also function as a carrier injection electrode.

Further, in the above-mentioned embodiment, the carrier supply J! J
Although the carrier supply layer 10.11 is sandwiched between the carrier supply layers 10.11 and 10.11, it is sufficient that either one of the carrier supply layers 10.11 is provided, and in that case, a carrier injection means may be provided in association with the carrier supply layer.

[Effects of the Invention] As described above, according to the electroluminescent device of the present invention, the total amount of carriers accumulated in the carrier supply layer is controlled, so the number of carriers that collide with and excite the luminescent center can be controlled. become able to. As a result, for example, it is possible to set the total amount of carriers for which the luminous efficiency is maximized, or to control the luminance. For display devices, etc.
It is possible to set the optimum brightness according to the usage environment, etc., and it is possible to contribute to improving the display quality of such a display device.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the basic structure of an electroluminescent device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view showing a conventional technique, and FIG. 3 is a cross-sectional view showing an example proposed by the inventors of the present invention. It is. 4... Light emitting layer, 10.11... Carrier supply layer, 2
0...Carrier injection electrode (carrier injection means) 1 Fig. 0a Fig. Broom diagram

Claims (1)

[Scope of Claims] An electroluminescent element in which a carrier supply layer for supplying carriers to the light emitting layer is laminated on the light emitting layer, characterized in that a carrier injection means for injecting carriers into the carrier supply layer is provided. Electroluminescent element.