JPS5821795B2 - Structure of thin film EL element - Google Patents

Description

Detailed Description of the Invention The present invention provides EL (Ele-ctr) by applying an alternating electric field.
The present invention relates to the structure of a thin film EL element that emits light (luminescence), and particularly relates to the electrode structure when producing a dielectric layer using a sputtering device such as a planar magnetron system.

Conventionally, for AC-operated thin-film EL devices, a high electric field (106 V/cfrL) is regularly applied to the light emitting layer to improve dielectric strength, luminous efficiency, operational stability, etc.
1-2.0 wt% Mn (or Cu.

Three-layer structure ZnS;Mn (or Zn5e:M
n) EL devices have been developed and improvements in light emitting characteristics have been confirmed.

This thin film EL element emits light with high brightness upon application of an alternating current of several KHz, and is characterized by long life.

It was also discovered that the light emission of this thin film EL element has a hysteresis characteristic in which the luminance of the light emitted by the same applied voltage differs in the process of increasing the applied voltage and in the process of decreasing the voltage from the high voltage side. In the process of increasing the applied voltage to a thin film EL element having hysteresis characteristics, when light, electric field, heat, etc. are applied, the thin film EL element
The element is excited to a state of luminescence brightness corresponding to its intensity,
It is known that there is a memory phenomenon in which the luminance remains in a high state even if light, electric field, heat, etc. are removed and the state is returned to its original state.

A thin film EL device application technology that effectively utilizes this memory phenomenon to utilize a thin film EL device as a memory device is currently being researched and developed in the industry.

FIG. 1 shows the basic structure of a ZnS:Mn thin film EL device as an example of a thin film EL device.

To specifically explain the structure of the thin film EL element based on FIG. 1, I n 203 and S n 02
Transparent electrode 2 such as
iO2, Al2O3, Si3N4. A first dielectric layer 3 made of SiO2 or the like is formed in an overlapping manner by sputtering, electron beam evaporation, or the like.

A ZnS light emitting layer 4 is formed on the first dielectric layer 3 by electron beam evaporation of ZnS:Mn sintered pellets.

At this time, the ZnS:Mn sintered pellets used for vapor deposition contain Mn, which is an active substance, at a concentration depending on the purpose.

A second dielectric layer 5 made of the same material as the first dielectric layer 3 is laminated on the ZnS light emitting layer 4, and an AI layer is further layered thereon.
A back electrode 6 is formed by vapor deposition.

The transparent electrode 2 and the back electrode 6 are arranged in directions perpendicular to each other and are connected to an AC power source 7 to drive the thin film EL element.

When an AC voltage is applied between the electrodes 2 and 6, the ZnS light emitting layer 4
The above AC voltage is induced between the dielectric layers 3 and 5 on both sides of the ZnS light emitting layer 4. Therefore, the electric field generated in the ZnS light emitting layer 4 excites electrons into the conduction band and accelerates them to obtain sufficient energy. , directly excites the Mn luminescent center, and emits yellow light when the excited Mn luminescent center returns to the ground state.

That is, when the electrons accelerated by a high electric field excite the electrons of the Mn atoms that have entered the Zn site, which is the luminescence center in the ZnS luminescent layer 4, and fall to the ground state, a wide wavelength spectrum with a peak of about 5850 A,% is generated. It emits strong light in the area.

The thin film EL element having the structure described above can be used as a flat thin display device that takes advantage of the space factor to display characters, symbols, still images, moving images, etc. in computer output display terminal equipment and various other display devices that contain characters and figures. It can be used as a means of displaying images, etc.

This thin film EL display device has an electrode structure composed of the transparent electrode 2 and the back electrode 6 shown in FIG. Display is performed using the position where the back electrodes 6 intersect in plan view as one pixel on the display screen.

Thin-film EL display devices have a lower operating voltage than conventional cathode ray tubes (CRTs), are superior in weight and strength compared to plasma display panels (FDPs), which are similar flat display devices, and are superior to liquid crystal (LCD) devices. ) has many advantages such as a wider operating temperature range and faster response speed.

Furthermore, since it is a pure solid matrix type panel, it has a long operating life, and its address accuracy makes it very effective as an input/output display means for computers and the like.

The dielectric layers 3 and 5 used in the thin film EL element are preferably made of materials with as high a dielectric constant as possible and a high dielectric strength voltage, since it is necessary to increase the effective electric field strength of the ZnS light emitting layer 4.

From this point of view, silicon nitride (S13N4), which is known as an amorphous thin film with few pinholes, is of good quality.

A sputtering method or an electron beam evaporation method is generally used to form the dielectric layers 3 and 5, but in recent years, a planar magnetron type sputtering device with a high sputtering rate has been developed. It is now used in the production of.

However, it has become clear that when the dielectric layer 3 is produced using this planar magnetron type sputtering apparatus, the light emitting characteristics of the thin film EL element are greatly influenced by the structure of the transparent electrode 2.

That is, the arrangement state of the transparent electrodes 2 is as shown in FIG. 1 as well as in FIG. The other end is buried inside the dielectric layer 3 without a mask, and the terminals for taking out the electrodes are taken out alternately from the opposite direction, and the pitch of taking out the electrodes is twice the pitch of the electrode arrangement. In the case of a configuration that facilitates connection, the light emitting state is not uniform on the display screen of the thin film EL element, and the brightness-voltage characteristics vary slightly along the stripe direction of the transparent electrode 2, causing the entire surface to emit light. In this case, it appears as uneven brightness.

The reason for this is that one end of the transparent electrode 2 is not masked, so when the substrate is exposed to discharge plasma, the direction of charges flowing along the stripe direction of the electrode generated by the incidence of secondary electrons alternates every other stripe. This is considered to be because the properties of the dielectric layer 3 laminated thereon differ slightly in the stripe direction due to the difference in the charge amount of the transparent electrode 2.

An object of the present invention is to provide a new and useful thin film EL element structure that effectively solves the above problems by making full use of technical means.

FIG. 3A is a plan view showing an array structure of transparent electrodes according to an embodiment of the present invention, and FIG. 3B is a side view of FIG. 3.

I n203 t S n formed on the glass substrate 1
A transparent electrode 2 such as 02 (NESA film) is coated with a dielectric layer 3 by masking both ends during sputtering.
Both ends extend outward, and as in FIG. 2, every other electrode is taken out at the end in the opposite direction.

With such a structure, uneven brightness can be prevented.

The reason is thought to be as follows.

When the substrate is made of an insulating material such as glass, as in a thin film EL device, in normal bipolar sputtering, the substrate is not only heated by the incidence of secondary electrons, but also charges are accumulated to form a bias potential. In this case, the sputtering operation becomes so-called bias sputtering.

The magnitude of this bias potential is the dielectric loss tangent (tan
δ), dielectric constant (ε), adhesion, etc.

On the other hand, a planar magnetron type sputtering device applies the Penning discharge phenomenon caused by a magnetic field 8 orthogonal to an electric field perpendicular to a flat plate target to a flat plate electrode, as shown in Fig. The sputtering efficiency is increased by performing the movement as shown in Figure 4.

In this method, it is thought that the number of secondary electrons incident on the glass substrate 1 is small, but it is not completely absent. Some secondary electrons are incident on the glass substrate 1, and sputtering is performed with a slight bias applied. be done.

Furthermore, in this sputtering method, the dielectric layer 3 must be fabricated by moving the glass substrate 1 over the target because it is necessary to make the film thickness distribution uniform in the plane direction.

Therefore, when the other end of the transparent electrode 2 is not masked as shown in FIG. 2, when moving over the target,
Each of the transparent electrodes 2 becomes electrically unequal to the adjacent electrode due to the difference in the amount of secondary electrons accumulated, and the bias is applied differently between the electrodes, resulting in changes in the characteristics of the dielectric layer 3. , a phenomenon called uneven brightness occurs.

The detailed mechanism regarding the physical behavior of incident secondary electrons remains unclear at present.

On the other hand, in the configuration in which both ends of the transparent electrode 2 are masked as in the present invention, when the substrate moves over the target, the parts of the transparent electrode 2 exposed to plasma are electrically equivalent, and each electrode has the same bias. Therefore, uneven brightness does not occur.

Furthermore, the characteristics of the dielectric layer 3 laminated on the transparent electrode 2 also become uniform.

The pattern shape of the end portion of the transparent electrode 2 extending outward from the dielectric layer 3 can be made into various shapes.

Further, each thin film deposited on the dielectric layer 3 can have the same structure as the conventional one.

It goes without saying that the configuration of the present invention can also be applied to processes other than planar magnetron sputtering.

As described in detail above, according to the present invention, the uneven luminance of the display screen is eliminated by a relatively simple means of extending the transparent electrode to the outside of the dielectric layer by masking both ends of the transparent electrode during sputtering. Improved quality can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic structure of a conventional thin film EL element. FIG. 2A is a plan view showing the arrangement of conventional transparent electrodes. FIG. 2B is a side view of FIG. 2A. FIG. 3A is a plan view showing an arrangement of transparent electrodes, explaining one embodiment of the present invention. FIG. 3B is a side view of FIG. 3A. FIG. 4 is a configuration diagram illustrating planar magnetron sputtering. DESCRIPTION OF SYMBOLS 1...Glass substrate, 2...Transparent electrode, 3...Dielectric layer.

Claims (1)

[Claims] 1. A thin-film EL device comprising an EL light-emitting layer mounted on a substrate with a dielectric layer interposed between matrix electrodes consisting of two sets of strip-shaped electrodes arranged in a direction perpendicular to each other. The one set of band-shaped electrodes interposed between the substrate and the dielectric layer has both ends extending outward from the dielectric layer, and every other electrode can be taken out from the opposite end. A structure of a thin film EL element characterized by comprising: