JPS5824915B2 - Thin film EL element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes EL (Ele-ctr) by applying an alternating electric field.
o Luminescence) Thin film E that emits light
The present invention relates to an L element, and in particular to a manufacturing technique for a thin film EL element that obtains good element characteristics by making full use of a new technology for the laminated structure of the thin film EL element.

Conventionally, for AC-operated thin film EL elements, a high electric field (about 10'v/cm) is regularly applied to the light emitting layer to improve dielectric strength, luminous efficiency, stability of operation, etc.
1-2. Ow tchi's Mn (or Cu y A
/ s B r etc.) doped ZnS.

Three-layer structure ZnS:Mn in which a semiconductor light emitting layer such as Zn5e is sandwiched between dielectric thin films such as Y203s TiO2
(or Zn5e:Mn) EL device has been developed, and it has been confirmed that the light emitting properties are improved.

This thin film EL element emits light with high brightness when an alternating current electric field of several KHz is applied, 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.

The structure of the thin film EL element will be explained in detail based on FIG.
A first dielectric layer 3 made of 3N4 e SiO□ 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 a ZnS:Mn sintered pellet.

At this time, the ZnS:Mn sintered pellet used for vapor deposition is a pellet in which Mn, which is an active substance, is set 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 A1
A back electrode 6 is formed by vapor deposition.

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

In other words, 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 strong emission occurs in a wide wavelength range with a peak of approximately 5850A. Exhibits luminescence.

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.

FIG. 2 shows an example of a conventional thin film EL panel.

This thin film EL panel has a matrix electrode structure in which the transparent electrode 2 and the back electrode 6 shown in FIG. The crossing position corresponds to one picture element on the panel when viewed from a plan view.

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

Since it is a pure solid matrix type panel, it has a long operating life, and its address accuracy makes it extremely effective as an input/output display means for computers, etc.

The dielectric layers 3 and 5 used in the thin-film EL panel are desirably made of materials with as high a dielectric constant as possible in order to increase the effective electric field strength of the ZnS light emitting layer 4, and from the viewpoint of improving stability, materials with low leakage current are preferred. , materials with high dielectric strength are desirable.

In an ideal case where there is no leakage current, the only current that flows through the device is, in principle, the displacement current (capacitive current), and there is no risk of the light-emitting layer being heated by unnecessary Joule heat, thus ensuring the stability of the device. It significantly contributes to improving sexual performance.

However, conventionally, as the material for this dielectric layer, films such as sio, 5i02p Gem2°Y2O3, TiO2, etc., have been used by electron beam evaporation or sputtering due to limitations in thin film production technology.

However, the dielectric properties of these thin films generally vary greatly depending on the formation conditions.

In other words, the strong crystallinity increases the occurrence of pinholes, and when the film stacked on the dielectric layer grows, the crystal grains have an adverse effect on the device breakdown voltage and the luminance of the light emitting surface. Becomes non-uniform.

In addition, it contains many physically and chemically unstable factors such as compositional deviation, decrease in packing density, and generation of microcracks.

In order to solve these problems, silicon nitride films, which are known as amorphous thin films, have recently come into use.

A silicon nitride film as a dielectric layer is usually formed by a sputtering method and has good breakdown voltage, so it is said to be one of the most suitable dielectric films for thin film EL devices.

However, this silicon nitride film still has some problems that need to be solved.

One of these is that the adhesion is weak, and the other is that interface states are easily formed.

The issue of adhesion has not yet been fully elucidated, or the bonding state with a different film may be due to the unique properties of the silicon nitride film or because it does not contain atoms with electronic bonding strength such as oxygen atoms. This is thought to be due to the fact that the bond is not due to bonding, but rather depends solely on van der Waals forces.

Therefore, if dirt, pinholes, impurities, etc. are present at the interface, this will result in peeling from that area.

In addition, due to slight differences in the surface condition of the substrates, irregular electron levels are formed at the interface, and as a result, the emission starting voltage becomes irregular within the light emitting surface, resulting in a light emission state with non-uniform luminance. .

In order to strengthen the adhesion of silicon nitride film,
As shown in FIG.
The 5i02 film 8 having a film thickness of about 600A is also coated with S
An Al2O3 film 9 or the like is interposed between the second dielectric layer 5 made of i3N4 and the back electrode 6 made of l' or the like, and by utilizing the electronic bonding force of the oxide film, the silicon nitride film is A structure with enhanced adhesion has been proposed.

However, when manufacturing a thin-film EL panel with such a structure, compared to the thin-film EL element shown in FIG.
The extra step of forming an oxide film for the i02 film increases the number of steps and complicates the control of processing conditions during manufacturing, which acts as an impediment to mass production on an industrial scale and increases costs. This may lead to disadvantageous results in terms of physical appearance, etc.

In view of the above-mentioned current situation, the present invention provides physically and chemically active 0.
By using a silicon oxynitride film containing an equivalent oxygen component of 1 to 10%,
A dielectric layer with optical adhesion can be easily obtained on a transparent electrode or glass substrate through a simplified manufacturing process by applying bonding force due to atomic reaction between the 5n02 or In2O3 film or the glass substrate. The purpose of the present invention is to provide a new and useful thin film EL device.

Another object of the present invention is to stabilize the device characteristics and extend the life of the device by coating it with a protective film that prevents moisture from entering from the surrounding environment.

One embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a cross-sectional configuration diagram of a display panel using thin film EL elements showing one embodiment of the present invention.

The thin film EL panel shown in FIG. 3 will be explained below according to the manufacturing process steps.

After cleaning the heat-resistant glass substrate 10 for a thin film EL panel made of 7059 Pyrex glass, etc.,
The transparent electrode 11 made of SnO2, In2O3, etc. has a film thickness of 1
Around 400-1500A, sheet resistance 10-20Ω/C1
Electron beam evaporation is performed to obtain 1L2.

In addition to this method, the transparent electrode 11 can be formed by spraying an aqueous solution of alcohol such as tin tetrachloride (SnC14) in the form of a mist onto a glass substrate heated to a temperature of 500° C. or higher, and then hydrolyzing and oxidizing it. In order to improve the uniformity and smoothness of the film surface, sputtering was performed using 5n02t In203 etc. as the cathode and a discharge in low pressure argon (Ar) gas, or tin (Sn) was used as the cathode (A
r +02 ) It can also be easily formed by a reactive sputtering method or the like in which an oxidation reaction is performed simultaneously with sputtering by discharging in a gas.

Next, in order to obtain a display pattern suitable for a thin-film EL panel, the transparent electrode 11 is etched using a photo-etching method to form one electrode group of the matrix electrode structure arranged in parallel in a band shape.

A first dielectric layer 12 is formed on the transparent electrode 11 and the surface of the glass substrate 10 exposed by etching.
Complex composition silicon oxynitride (Si 11con-Oxyni-tride) containing 1-10% equivalent 5i02
) A film is formed with a thickness of 0.1 to 10 μm by sputtering.

The silicon oxynitride film is formed by using nitrogen gas mixed with an appropriate amount of 0.1 to 10% nitrous oxide (N20) or oxygen (0□) as the working gas for sputtering, and using high-purity polycrystalline silicon or sputtering target as the sputtering target. Using a high-purity sintered silicon nitride plate, through an operation process mainly based on high-frequency discharge with a power density of several to several tens of watts on the target, the sputtering effect of ions and the reaction result of the working gas are It is done.

At this time, the activity of oxygen is considerably higher than that of nitrogen gas, so the amount of oxygen contained in the dielectric layer is relatively larger than the amount of oxygen mixed into the working gas. The content in the nitride thin film is approximately 0.1 to 10%.

This dielectric layer containing oxygen atoms has an effect on the adhesion of the interface.
In addition to van der Waals forces, the electronic bonding force of oxygen atoms contributes, so strong adhesion is obtained, and the interfacial state is very good, so that the formation of interfacial states is largely suppressed.

Furthermore, if the amount of nitrous oxide gas mixed in is properly controlled, the electrical characteristics will not change and the amorphous film quality will not be impaired.

When the amount of nitrous oxide gas mixed in exceeds 5%, the formed film will contain silicon oxide (SiO2) or become a complete silicon oxide film, the dielectric constant will decrease, and the film quality will become crystalline. .

Therefore, it is desirable to set the amount of nitrous oxide mixed in to an appropriate value, that is, within the range of 0.1 to 2.0%, depending on the sputtering conditions.

On the first dielectric layer 12 obtained through the above operation process, a ZnS light emitting layer 13 doped with Mn is added in an amount of 0.01 to 20%.
Vacuum evaporation is performed to a film thickness of μm.

The ZnS light emitting layer 13 is formed at 10-7 to 10-3 tor.
This is carried out by depositing ZnS:Mn sintered pellets using an electron beam or the like in a vacuum of about r.

At this time, in order to impart memory characteristics to the thin film EL element, it is necessary to appropriately control the dopant concentration, that is, the Mn concentration, in the ZnS light emitting layer 13.

According to experimental results, a memory phenomenon begins to occur when the Mn concentration of the deposition pellets used for manufacturing the ZnS light emitting layer 13 exceeds approximately 0.5 wt%, and the effect becomes more pronounced as the Mn concentration increases. found.

In addition, the ZnS light emitting layer 13 can be formed by vapor deposition by resistance heating other than the above, or by turning Mn-added ZnS into a powder with uniform particle size, dropping it little by little into a boat heated to a high temperature, and instantaneously evaporating it. It can also be carried out by flash vapor deposition or the like.

According to this method, a uniform film without compositional deviation can be formed.

The above-mentioned sputtering method or vacuum evaporation method or C, V-D (Chemical
Vapor Deposition) method etc.
A dielectric layer 14 is formed.

The second dielectric layer 14 is made of a silicon oxynitride film containing 0.1 to 10% equivalent SiO2 or Si3N4 like the first dielectric layer 12 in consideration of dielectric strength. Formed with p Y203 or the like.

Further, on the surface of the second dielectric layer 14, a physically and chemically stable Al having water resistance is coated to prevent moisture from entering.
A protective film 15 made of 2O3 or the like is coated.

The thin film EL panel shown in FIG. 3 is manufactured by depositing a back electrode 16 made of A1 or the like on the protective film 15 and connecting the back electrode 16 and the transparent electrode 11 to a power source.

Like the transparent electrodes 11, the back electrodes 16 are processed into strips by photoetching, and are arranged in parallel in a direction perpendicular to the arrangement direction of the transparent electrodes 11 to constitute the other electrode group of the matrix electrode structure.

The thin film EL panel having the above structure has a three-layer structure in which the ZnS light emitting layer 13 is sandwiched between the dielectric layers 12 and 14, and the dielectric layers 12 and 14 are composed of high voltage insulating layers. It is possible to stably apply a high electric field equivalent to the amount of light to the layer 13, resulting in a display panel with stable luminance and long-term use.

Further, this three-layer structure is covered with a water-resistant protective film 15 to protect the ZnS light-emitting layer 13 from the atmosphere, especially moisture.

This protective effect can be achieved by using Ta205 or Al2 as the protective film 15.
This is particularly noticeable when O3 is used, and greatly contributes to improving the stability and increasing the lifespan of thin-film EL panels.

The thin film EL panel in Figure 3 has a transparent electrode 11 and a back electrode 1.
By applying a bipolar pulse to 6 via a control circuit, a drive circuit, etc., display is driven in units of picture elements, with the point where both electrodes 11 and 16 intersect being one picture element.

The display image is TV (Televis-ion).
) It is possible to obtain moving images from a video device, etc., still images of characters, symbols, figures, etc. from an output terminal device, etc., or still images obtained by grasping and stopping a moving image at a certain moment.

In addition to the structure described above, the structure of the thin film EL device according to the present invention can also be a structure in which multicolor light emission and mixed color light emission are obtained by forming multiple light emitting layers with different light emission colors to which various active substances are added. Depending on the configuration, a color display can be produced.

Although the above embodiments have been described using nitrous oxide or oxygen gas as the mixed gas for the working gas, it is of course possible to achieve the object of the present invention by using other oxidizing gases.

As explained in detail above, according to the present invention, by forming the dielectric layer with a silicon oxynitride thin film, the adhesion of the interface is increased, and the substrate surface requires a high degree of cleanliness and smoothness. A homogeneous and stable dielectric layer can be obtained.

Therefore, the layer interface state of the dielectric layer in contact with the transparent electrode becomes stable, and a protective film is interposed between the dielectric layer on the back electrode side and the back electrode, so that a high electric field is applied to both dielectric layers. In contrast, the dielectric strength is significantly improved, and uniform luminance can be obtained over the entire light emitting surface.

Furthermore, the thin film EL element structure of the present invention, which exhibits stable insulation at the layer interface between the dielectric layer and both electrodes, can be a very effective technology even when used in a memory element where a high electric field is applied during writing. It is something.

In addition to the above, the protective film coated on the dielectric layer has the effect of effectively protecting the thin film EL element from the surrounding environment, especially moisture, dirt, dust, and the like.

Particularly when the back electrodes are constituted by matrix electrodes, the dielectric layer is prevented from being exposed to the outside through the gap between the back electrodes, thereby preventing adverse effects from the surrounding environment from reaching the inside of the element.

Therefore, it can contribute to improving the operating life of the thin-film EL panel, and it becomes easier to handle when manufacturing the panel.

In addition, looking at the present invention from a manufacturing perspective, a high-quality dielectric layer with strong adhesion can be obtained in a single-layer vapor deposition process, which simplifies the manufacturing process and makes it easier to control the manufacturing processing conditions in the manufacturing process. This form is suitable for mass production lines.

Therefore, manufacturing costs can be significantly reduced.

The thin film EL panel obtained through the manufacturing process of the present invention is
It can be used in a wide range of applications as a highly reliable, long-life display panel that is unaffected by the usage environment and can withstand even harsh conditions. This can serve as a highly meaningful display panel.

[Brief explanation of the drawing]

Figure 1 shows an example of a conventional thin-film EL device using ZnS:M.
1 is a cross-sectional configuration diagram showing the basic structure of an n-thin film EL element. FIG. 2 is a cross-sectional configuration diagram of a conventional thin film EL panel. FIG. 3 is a cross-sectional configuration diagram of a display panel using thin film EL elements showing one embodiment of the present invention. 11... Transparent electrode, 12... First dielectric layer, 13
. . . ZnS light emitting layer, 14 . . . second dielectric layer, 15
...Protective film, 16... Back electrode.

Claims (1)

[Claims] 1 It has a three-layer structure consisting of a thin-film light-emitting layer doped with an active substance and first and second dielectric layers laminated on both sides of the thin-film light-emitting layer. In a thin film EL device in which the first dielectric layer superimposed on the silicon oxynitride film is a silicon oxynitride film, a second electrode that applies a voltage to the third layer structure together with the first electrode; 1. A thin film EL device, characterized in that an insulating protective film having water resistance is formed, and the surface of at least the second dielectric layer of the three-layer structure portion is covered with the insulating protective film.