JPH0577160B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a thin film electroluminescent device that emits light upon application of an electric field.

[Background technology]

Phosphor thin film emitting layers such as zinc sulfide or zinc selenide added with manganese or rare earth fluorides, calcium sulfide or strontium sulfide added with rare earth elements, yttrium oxide, silicon oxide, tantalum oxide, aluminum oxide, silicon nitride, etc. Thin-film electroluminescent devices sandwiched between two dielectric layers made of barium titanate, lead titanate, strontium titanate, etc. have already achieved luminance of 5000 cd/m ²
As described above, a luminous efficiency of 8 m/W has been achieved. However, such thin-film electroluminescent devices require high AC voltage (100 V or more) as a driving power source, so there is no freedom in selecting a driving method and it is difficult to link them with other devices.

Therefore, as an alternative to such a high voltage type element, a device in which electrodes are brought into direct contact with both surfaces of a phosphor thin film light emitting layer has been considered. This type of thin-film electroluminescent device does not require the application of a high alternating current voltage like conventional devices, and can be driven with a low direct current voltage, which increases the flexibility in selecting a driving method and allows for integration with other devices. Collaboration will also be free.

Among these types, those containing a conductive material such as copper in a phosphor thin film light-emitting layer made of zinc sulfide added with manganese or rare earth fluoride can be operated at a lower voltage.

One of the applications of thin-film electroluminescent devices is X-Y dot matrix for television displays and the like.
This device has two sets of band-shaped electrodes formed on both sides of a phosphor thin film light-emitting layer so as to intersect with each other. The part of the layer sandwiched between two strip electrodes to which a voltage is applied (pixel part)
emits light, and a predetermined display is made as a whole.

FIG. 3 shows an example of such a matrix-like thin film electroluminescent device. In the thin film electroluminescent device of this example, a first band-shaped electrode group 2 is provided on a substrate 1, and a continuous phosphor thin film light emitting layer 3' is formed thereon over all predetermined pixel portions. ,
Furthermore, a second band-shaped electrode group 4 is provided thereon.

When using a phosphor thin film light-emitting layer containing a conductive material such as the aforementioned copper, it is necessary to perform a forming treatment upon completion of the device in order to stabilize the light emission. This forming process involves applying a constant voltage to the phosphor thin film light emitting layer.
This process forms a high-resistance layer inside it. At the first stage of the forming process, a large current flows because the resistance value of the phosphor thin film light emitting layer is low. The total current I _T at that time has a relationship of I _T =I _U ·S, where I _U is the current per unit area and S is the light emitting area.

However, in the configuration shown in FIG. 3, the total current I _T is usually much larger than I _U ·S,
Current loss becomes enormous.

Furthermore, in the thin film electroluminescent device having the configuration shown in FIG. 3, when in use, the area around each pixel portion 3'a emits light, causing the pixels to become blurry and making it impossible to display a clear pattern. There is also the problem of reduced efficiency.

These problems are caused by the fact that the specific resistance of the phosphor thin film light emitting layer 3' other than each pixel portion 3'a (the area surrounded by the dashed line in the figure) is the specific resistance between the upper and lower strip electrodes 2 and 4; In other words, it is considered that the reason is that the resistivity is as low as the specific resistance of the pixel portion 3'a. That is, when a voltage is applied between the upper and lower strip electrodes 2 and 4 to cause the pixel portion 3'a to emit light, part of the current flowing between these electrodes that should cause the pixel portion 3'a to emit light is as shown in the figure. As shown by the arrow, the light leaks and flows to parts other than the pixel part 3'a, thereby causing the blurring, loss, and reduction in efficiency.

Therefore, in order to eliminate such problems, a thin film type electroluminescent device having a structure as shown in FIG. 4 was devised. As shown in the figure, this device has a phosphor thin film light-emitting layer separated into each pixel portion 3''a.
This prevents leakage current from flowing between pixels.

However, normally the phosphor thin film emitting layer has a thickness of 1 to 4 μm.
In contrast, the strip electrode formed thereon has a thickness of only about 2000 Å, and moreover, at the edge portion of the phosphor thin film light emitting layer 3″a,
Since the strip electrode 4 becomes even thinner, there is a risk of wire breakage. In a structure in which the phosphor thin film light-emitting layer is separated as shown in FIG. 4, the risk increases in proportion to the number of pixels, so there is a problem that sufficient reliability cannot be obtained.

[Purpose of the invention]

This invention has been made in view of the above circumstances, and since there is no leakage current, there is no fear of current loss, blurring, or reduction in luminous efficiency during forming or use, and the thin film has sufficient reliability. The object of the present invention is to provide a type electroluminescent device.

[Disclosure of the invention]

In order to achieve the above object, the present invention provides a method in which a phosphor thin film light-emitting layer is sandwiched between two sets of band-shaped electrode groups provided to intersect with each other, and at least one set of band-shaped electrode groups is formed of a transparent conductive film. A thin film electroluminescent device, in which a material for increasing conductivity is contained only in a pixel portion of the phosphor thin film light emitting layer where one set of strip electrodes intersects the other set of strip electrodes. The gist of this paper is a thin film electroluminescent device characterized by:

Hereinafter, the present invention will be explained in detail with reference to the drawings showing one embodiment thereof. Note that in these figures, the upper and lower strip-shaped electrode groups are composed of two to three strip-shaped electrodes, but this is merely a schematic representation of the configuration. Since the actual number of pixels is large, the number of band-shaped electrodes that make up the band-shaped electrode group is also large.

As shown in FIG. 1, the structure of the thin film electroluminescent device of this embodiment is almost the same as that of the conventional device having a continuous phosphor thin film light emitting layer. That is,
A first band-shaped electrode group 2... is provided on the substrate 1,
A continuous phosphor thin film light emitting layer 3 is formed thereon, and a second band-shaped electrode group 4 . . . is further formed thereon.

Therefore, according to this configuration, there is no risk of the strip electrode being disconnected as in the one shown in FIG. 4, and reliability is high. At the edge of the phosphor thin film light emitting layer 3,
There is still a risk of disconnection, but in that case,
For example, if the thickness around the phosphor thin film light-emitting layer 3 is changed gently so that it is connected to the surface of the substrate 1, no edge portion is formed, thereby making it possible to further improve reliability. At this time, if the change in film thickness is applied to the pixel portion 3a, the light emitting performance will be affected, so the change in film thickness may be started from a location outside the pixel portion 3a.

As the substrate 1, the same materials as conventional ones, such as alkali-free glass, can be used.

At least one of the first and second strip-shaped electrode groups 2..., 4... needs to be formed of a transparent conductive film because it is necessary to extract light to the outside of the element.
The other may be a transparent conductive film or may be a simple metal film.

As the material for the transparent conductive film, ordinary materials such as tin oxide, indium oxide, indium oxide (ITO) added with tin oxide, zinc oxide, and zinc oxide added with aluminum oxide can be used. For example, when forming a transparent conductive film made of ITO using the high frequency sputtering method, as a target,
Indium oxide sintered bodies containing about 10 mol % of tin oxide are generally used. These transparent conductive films can be formed by the above-mentioned high frequency sputtering method or electron beam evaporation method, and the film thickness is preferably about 3000 Å.

As the metal film, ordinary electrode materials such as aluminum and gold can be used. These metal films can be formed by vacuum evaporation, and the film thickness is preferably about 2000 Å.

As mentioned above, zinc sulfide to which manganese or rare earth fluoride is added is mainly used as the phosphor thin film light emitting layer 3, but other phosphors may also be used. In the above configuration, the amount of manganese etc. added to zinc sulfide is 0.5% by weight.
degree is preferred.

Such a phosphor thin film light-emitting layer 3 normally contains a conductive material such as copper throughout, but in the present invention, as shown in FIG. It is characterized in that such a conductive material is contained only in the intersecting part, that is, in the pixel part 3a surrounded by the dashed line in the figure.

In this way, in order to include a conductive material such as copper only in the pixel portion 3a, the following method may be used, for example.

First, on the part corresponding to the pixel on the band-shaped electrode group 2 formed on the surface of the substrate 1 by a predetermined method,
A thin copper film of about 30 to 300 Å is deposited by a method such as a vacuum evaporation method or a high frequency sputtering method.

Next, the substrate 1 and each strip electrode 2 are formed by a method such as an electron beam evaporation method or a high frequency sputtering method.
A continuous phosphor thin film light-emitting layer 3 with a thickness of about 1 to 4 μm is formed so as to cover...

Then, when heating is performed at 600 to 650°C for about 1 to 4 hours in a vacuum or an inert gas such as argon gas or nitrogen gas, the copper is thermally diffused into the pixel portion 3a and is contained therein. It can be done.

The formation of the copper thin film and the formation of the phosphor thin film light emitting layer 3 may be performed in the reverse order, or the copper thin film may be formed above and below the phosphor thin film light emitting layer 3.

Thereafter, by forming band-shaped electrode groups 4 on the phosphor thin-film light-emitting layer 3 so as to intersect with the band-shaped electrode groups 2, a thin-film type electroluminescent device is obtained.

In the thin film electroluminescent device of the present invention formed as described above, as described above, only the pixel portion 3a contains a conductive material such as copper, so that the conductivity of this portion and the phosphor There is a significant difference in conductivity from other parts of the thin film light emitting layer 3. For example, a phosphor using zinc sulfide doped with manganese or the like has ^a specific resistance of about 10 ¹⁰ to 10 ¹¹ Ωcm when copper is not included, whereas it has a resistivity of about 10 10 to 10 11 Ωcm when copper is included. The specific resistance is as low as ~10 ⁵ Ωcm, and even after the forming process, it is around 10 ⁵ - ^{10 7} Ωcm. Therefore, when a voltage is applied between the strip electrodes 2 and 4, a current flows through the pixel portion 3a as indicated by the arrow in FIG. 1, but this current does not leak to other portions. This prevents current loss, blurring, and reduction in luminous efficiency.

As an example, number of pixels is 50×50, pixel size is 0.2×
A thin film electroluminescent device with a pixel pitch of 0.2 mm and a pixel pitch of 0.2 mm was made with the configuration shown in Figures 1 and 3, and a voltage of 15 to 30 V was applied so that the upper band-shaped electrode group 4... side had a positive potential. The forming process was performed. Then, in the conventional configuration shown in Fig. 3, the entire phosphor thin film light-emitting layer 3' contains copper and has a low resistivity, so a forming current of up to 4 A is required. In the device having the configuration of the present invention shown in FIG. 1, the forming current was only about 1A, which is about 1/4 of that of the conventional device, and the forming effect was almost unchanged.

〔Effect of the invention〕

The thin film electroluminescent device of the present invention is as described above, in which a phosphor thin film light emitting layer is sandwiched between two sets of band-shaped electrode groups provided to intersect with each other, and at least one set of band-shaped electrode groups is transparent. A thin-film electroluminescent device formed of a conductive film, in which conductivity is increased only in a pixel portion of the phosphor thin-film light-emitting layer where one set of strip-shaped electrodes and the other set of strip-shaped electrodes intersect. The material contains no leakage current, so there is no risk of current loss, blurring, or reduction in luminous efficiency during forming or use, and it has sufficient reliability.

[Brief explanation of the drawing]

FIG. 1 is a layer structure diagram schematically showing the layer structure of an embodiment of the thin film electroluminescent device of the present invention, and FIG.
The figure is a perspective view, FIG. 3 is a layer structure diagram schematically showing an example of a conventional thin film electroluminescent device, and FIG. 4 is a layer structure schematically showing another example of a conventional thin film electroluminescent device. It is a diagram. 2, 4... Strip electrode, 3... Phosphor thin film light emitting layer, 3a... Pixel portion.

Claims (1)

[Claims] 1. A thin film electroluminescent device in which a phosphor thin film light-emitting layer is sandwiched between two sets of band-shaped electrode groups arranged to intersect with each other, and at least one set of band-shaped electrode groups is formed of a transparent conductive film. , a thin film type electroluminescence characterized in that a material for increasing conductivity is contained only in a pixel portion of the phosphor thin film light emitting layer where one set of strip electrodes intersects with the other set of strip electrodes. element.