JPS5944633B2 - Thin film EL panel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes EL (Electro
The present invention relates to a deterioration prevention structure for thin film EL panels, which is an effective technology for EL display panels using thin film EL elements that emit luminescence.

Conventionally, for AC-operated thin film EL elements, a high electric field (about 106 V/cm) is regularly applied to the light emitting layer to improve dielectric strength, luminous efficiency, stability of operation, etc.
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A three-layer structure ZnS:Mn (or ZnSe:Mn) EL device sandwiched between dielectric thin films such as 2O3 and TiO2 has been developed, and improvements in various light-emitting properties have been confirmed.

This thin film EL element emits light with high brightness when an alternating current electric field of several KH2 is applied, and is characterized by long life. In addition, regarding the light emission of this thin film EL element, there are two processes: increasing the applied voltage and decreasing it from the high voltage side.
It was discovered that the thin-film EL element has a hysteresis characteristic in which the luminance differs for the same applied voltage, and in the process of increasing the applied voltage to a thin-film EL element with this hysteresis characteristic, light, electric field, and heat When the light, electric field, heat, etc. are removed and the element returns to its original state, the thin film EL element is excited to a state of luminance corresponding to the intensity, and the luminance remains high even if the light, electric field, heat, etc. are removed and the element returns to its original state. The so-called memory phenomenon has opened up new fields of use for display technology.
FIG. 1 shows the basic structure of a ZnS:Mn thin film EL device as an example of a thin film EL device. The structure of the thin film EL element will be explained in detail based on FIG.
A first dielectric layer 3 made of , SiO2 or the like is formed in an overlapping manner by sputtering or electron beam evaporation.

A ZnS light-emitting layer 4 is formed on the first dielectric 5 layer 3 by electron beam evaporation of ZnS:Mn sintered pellets. At this time, the ZnS:Mn sintered pellets used for vapor deposition are pellets in which the concentration of Mn as an active substance is set to suit 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 a back electrode 6 made of Al or the like is further deposited thereon.

The transparent electrode 2 and the back electrode 6 are connected to an AC power source 7, and the thin film EL element is driven. When an AC voltage is applied between the electrodes 2 and 6, the above AC voltage is induced between the dielectric layers 3 and 5 on both sides of the ZnS light emitting layer 4, and therefore the electric field generated within the ZnS light emitting layer 4 Therefore, the electrons excited and accelerated into the conduction band and having obtained sufficient energy directly excite the Mn luminescent center, and when the excited Mn luminescent center returns to the ground state, it emits yellow light. That is, electrons accelerated by a high electric field reach Z, which is the luminescent center in the ZnS luminescent layer 4.
When the electrons of the Mn atoms that have entered the n-site are excited and fall to the ground state, they emit strong light in a wide wavelength range with a peak of approximately 5850N. Thin film EL with the above structure
The element can be used as a flat thin display device that takes advantage of the advantages of the Spanish factor, and can be used as a means of displaying characters, symbols, still images, moving images, etc. in computer output display terminal equipment and various other display devices that contain characters and figures. can do.

A thin film EL panel used as a flat flat display device has a lower operating voltage than a conventional cathode ray tube CRT, and is superior in terms of weight and strength compared to a plasma display panel PDP, which is the same flat display device. It has many advantages over liquid crystal LCDs, such as a wider operating temperature range and faster response speed. Furthermore, since it can be used as 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.
3 However, the dielectric layer of the thin film EL element contains many pinholes and microcracks generated during the manufacturing process, and moisture, etc. enters the ZnS light emitting layer 4 through these defects, resulting in heat generation due to EL emission loss, This results in deterioration of device characteristics. 4. In order to solve the above problem, as shown in FIG. 2, Si3N4 film or A
A structure is implemented in which the insulating film 8 such as an 12O3 film is coated to protect it, or a structure in which a resin 9 is further coated on the insulating film 8 to protect it. Furthermore, a vacuum-sealed structure has been proposed. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals, and their explanation will be omitted.

However, when forming a protective film by coating each of the thin films 3, 4, and 5 constituting the thin film EL element with the insulating film 8, pinholes are easily formed due to the adhesion of microscopic dust, foreign matter, etc. As the area increases, there are drawbacks such as difficulty in producing a uniform protective film free of defects.

Furthermore, even if a complete protective film is formed, imperfections in a minute area of the thin film EL element will cause breakdown on the light emitting surface when electricity is applied, and as a result, the protective film will be damaged due to thermal damage in the minute area. After the damage occurs, moisture in the atmosphere, which is thought to be the main cause of destruction and deterioration of the thin film EL element, leaks from the damaged area.
Penetrates into the luminescent layer. In order to realize a protection method using a thin film coating, both the thin film EL element and the protective film must be completely uniform, but the current thin film production technology is capable of producing sufficiently dense EL elements without any structural defects.
Producing the emissive and dielectric layers is extremely difficult and not a practical method.

On the other hand, in vacuum sealing, there is the problem of deterioration of the degree of vacuum due to outgas when thermal breakdown occurs due to breakdown due to the imperfection of the thin film EL element mentioned above, and the complexity of the vacuum sealing process. There are drawbacks. In addition, both thin film coating and vacuum sealing have drawbacks such as inability to dissipate heat generated due to EL emission loss. Regarding the coagulable resin coating, if the resin and the thin film EL element have strong adhesion, vibrations generated during energization, stress distortion during handling, thermal stress distortion, etc. will have an adverse effect such as delamination of the thin film EL element. On the other hand, if the adhesion is weak, gaps may occur due to vibration, deflection, and heat generation, making it impossible to prevent moisture from entering the atmosphere. In view of the above-mentioned drawbacks, we have taken measures to prevent and fix the expansion of minute thermal damage areas that occur due to breakdown caused by pinholes and other imperfections that occur during energization, and to protect against moisture in atmospheric environments. A sealing method using fluids such as oil has been proposed as a sealing method that is effective in improving heat dissipation effects, as well as vibration and deflection.

FIG. 3 shows an example of a thin film EL panel using this fluid injection sealing method.

This thin film EL panel adopts a matrix electrode structure in which the transparent electrode 2 and the back electrode 6 shown in FIG. The intersecting position corresponds to one pixel of the panel when viewed from a plan view. To explain based on FIG. 3, a transparent electrode 2, a first dielectric layer 3, and a ZnS light emitting layer 4 arranged in parallel on a glass substrate 1 are sequentially laminated, and on the ZnS light emitting layer 4, an Sl3N4 film and a Sl3N4 film are formed. A second dielectric layer 5 consisting of an Al2O3 film superimposed on the film is laminated in a two-layer structure, and a back electrode 6 arranged in parallel in a direction orthogonal to the transparent electrode 2 is further formed on the second dielectric layer. set on top,
A thin film EL element is constructed.

In order to seal this thin film EL element, a back glass plate 11 is arranged to face the glass substrate 1 with a spacer 10 in between, and each joint of the glass substrate 1, spacer 10, and back glass plate 11 is fixed with an adhesive 12. It is sealed and forms an envelope for the thin film EL device. A thin film EL element is housed in the envelope, and an injection fluid 13 for protecting the thin film EL element, such as silicone oil or vacuum grease, is filled and sealed. The conditions required for the injection fluid 13 are (1)
Penetrates into pinholes, (2) has high dielectric strength,
(3) It is desirable that it has excellent heat resistance and moisture resistance, (4) it does not react with the constituent films of thin film EL elements, and (5) it is a fluid substance with vapor property and a small coefficient of thermal expansion, but it is especially suitable for pinholes. It is required to have permeability, have a certain high dielectric strength voltage, and not react with the films constituting the thin film EL element. As the spacer 10, an insulating plastic sheet such as Teflon or polyimide resin having a thickness of 0.5 m71 L is used, but silicone rubber, glass, etc. may also be used. The spacer 10 is provided with one to several micro injection holes 14 for injection of silicone oil, etc., around the spacer 10 . The injection hole 14 may be formed in the back glass plate 11. Epoxy resin or the like is used as the adhesive 12, and the adhesive 12 is attached to the joints of the envelope except for the injection hole 14. In addition, the transparent electrode 2 and the back electrode 6
The lead terminal portion 15 is connected to the glass substrate 1 and the back glass plate 11.
One end thereof extends onto the glass substrate 1 outside the envelope through the joint portion, and is electrically connected to a drive control circuit (not shown). When an alternating current voltage is applied through the transparent electrode 2 and the back electrode 6, a light emitting display is performed on a pixel-by-pixel basis from the front surface of the glass substrate 1. Since the thin film EL panel having the above structure can effectively prevent moisture from entering the atmosphere, it has an excellent effect of dramatically improving the reliability and life of the thin film EL element.

However, even with the above configuration, there still remains the problem that the injected fluid itself, such as sealing oil, contains moisture, and this moisture enters the thin film EL element and becomes a factor in deteriorating the characteristics of the element. It is technically difficult to completely remove moisture contained in the injection fluid before injection, and even after performing a gas venting operation, some moisture remains in the injection fluid.
In view of the above-mentioned problems, the present invention has been devised to provide a new and useful product that completely protects the thin-film EL element from moisture by adsorbing the water contained in the injection fluid for protecting the thin-film EL element to an absorber, thereby establishing further reliability. The purpose is to provide a thin film EL panel.

Hereinafter, the present invention will be explained in detail according to embodiments with reference to the drawings.

FIG. 4 is a cross-sectional configuration diagram of essential parts of a thin film EL panel showing one embodiment of the present invention.

The same reference numerals as in FIG. 3 indicate the same contents, and the explanation will be omitted. As in FIG. 3, a thin film EL element is housed in an envelope, and filled with injection fluid 13 such as silicone oil or vacuum grease.

A moisture absorber 16 made of aluminum foil coated with silica gel is pasted in the form of a sheet on the inner surface of the rear glass plate 11 constituting the envelope. Since the injection fluid 13 is nonionic, silica gel can adsorb ionic water without being hindered by the injection fluid. Moisture absorber 16
is adhered to the rear glass plate 11 with epoxy resin or the like.
The person injecting the fluid into the envelope should heat both to 10"C~2" after adhering the envelope.
After raising the temperature to 00 DEG C. and degassing under a reduced pressure of 10@-2 T0rr or less, the injection hole 14 is inserted into a bath of silicone oil or the like. After the fluid is injected, the injection hole 14 is sealed with epoxy resin or the like. Although the moisture absorber 16 is made of aluminum foil coated with silica gel, it may be coated on glass or plastic, or a sheet of silica gel alone may be directly attached to the back glass 11. FIG. 5 is a characteristic diagram showing the state of deterioration when ten thin film EL panels shown in FIG. 3 and ten thin film EL panels shown in FIG. 4 were extracted and subjected to an accelerated test in a heated and humid atmosphere.

In the figure, a is a deterioration curve of a conventional thin film EL panel that does not contain silica gel, and b is a deterioration curve of the thin film EL panel shown in the above embodiment that contains silica gel. In the figure, c indicates a limit region where display quality begins to deteriorate. Thin-film EL panels containing silica gel have an element life that is four to five times longer than conventional panels. In this experiment, the silica gel was set to have a thickness of 100 μm or less, but the life will be further extended if the silica gel layer thickness is increased. Figure 6, Figure 7,
FIG. 8 is a cross-sectional view of the main part of a thin film EL panel showing other embodiments of the present invention.

In the embodiment shown in FIG. 6, a template 17 made of plastic or the like is installed around the outer periphery of the thin film EL element in the envelope, and a spacer 18 is interposed between the template 17 and the rear glass plate 11, and the spacer 18 separates the element. A moisture absorber 16 made of silica gel powder is inserted into the gap between the mold plate 17 and the back glass plate 11.

Although it is possible to provide a moisture absorbing function by simply mixing fine silica gel powder into the injection fluid 13, in this case, the display quality will deteriorate due to precipitation, so it is not necessary to It is desirable to use the template 17 to make the silica gel invisible from the front (display side) glass substrate 1. In the embodiment shown in FIG. 7, a moisture absorber 16 made of silica gel powder filled in a tube with two microscopic holes or a large moisture-permeable tube is arranged around the inside of the envelope. It is something. Figure 8 shows spacer 1
Silica gel is contained in the resin constituting 0.

Although the moisture absorption effect is slightly inferior to those of the above embodiments, the structure is simplified. As explained in detail above, according to the present invention, the fluid for protecting thin film EL elements injected into the thin film EL panel not only prevents moisture in the atmosphere from entering the thin film EL elements, but also prevents moisture contained in the fluid itself from entering the thin film EL elements. Since it is adsorbed by the moisture absorber inside, the effect of preventing moisture from entering into the thin film EL element becomes even more remarkable, and the display life of the thin film EL panel is dramatically improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a specific structure of a thin film EL element. FIG. 2 is a block diagram of a conventional thin film EL element. FIG. 3 is a diagram illustrating a main part of an example of a conventional thin film EL panel.
FIG. 4 is a cross-sectional configuration diagram of essential parts of a thin film EL panel for explaining one embodiment of the present invention. FIG. 5 is a characteristic diagram showing the results of a deterioration test for the thin film EL panels shown in FIGS. 3 and 4. FIG.
FIG. 6, FIG. 7, and FIG. 8 are sectional views showing main parts of a thin film EL panel showing other embodiments of the present invention. 1・
...Glass substrate, 10...Spacer, 1
1...Back glass plate, 16...Moisture absorber.

Claims (1)

[Claims] 1. In a thin-film EL panel in which a thin-film EL element is built in an envelope consisting of a translucent front substrate and a back plate, and display is performed via the translucent front substrate, Injecting a sealing oil that prevents moisture from entering the thin film EL element and disposing a moisture absorber in contact with the sealing oil, so that moisture contained in the sealing oil is adsorbed by the moisture absorber. A thin film EL panel featuring: