JPH01225093A - Manufacture of electroluminescence element - Google Patents

Abstract

PURPOSE:To obtain an EL element with low driving voltage and a long life and hardly having dielectric breakdown in the continuous use by constituting at least part of insulating layers inserted between mating electrodes and a phosphor layer with a specific silicon nitride thin film. CONSTITUTION:A phosphor layer 4 and insulating layers 3 and 5 are arranged between mating electrodes 2 and 6 at least one of which is transparent, at least part of the insulating layers is constituted with a silicon nitride thin film with the thickness of 2.000Angstrom or below and formed by the plasma CVD method, silane gas and ammonia gas diluted by hydrogen gas are used at the flow ratio (volume) of 5 or above between ammonia gas and silane gas as the source gas in the plasma CVD method. The silicon nitride thin film is made a very fine insulating film layer, when at least part of the insulating layer of an electro luminescence EL element is constituted with this silicon nitride thin film, the driving voltage is sharply reduced, dielectric breakdown hardly occurs in the long-term continuous use, no propagation type dielectric breakdown occurs under severe conditions, and a long life is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electroluminescent (hereinafter referred to as EL) element used in display devices and the like.

[Conventional technology]

This type of EL element has a structure between a pair of electrodes, at least one of which is transparent and usually one of which is patterned.
It has a structure in which a light emitter layer and an insulating layer adjacent to it are interposed, and there is a table insulation type in which the insulating layer is provided on only one side of the light emitter layer, and a double insulation type in which the insulating layer is provided on both sides. In addition, the luminescent layer is not limited to one layer, and there are also devices in which two or more layers are laminated with an insulating layer interposed therebetween. To drive such an EL element, an alternating current electric field higher than the emission starting voltage of the luminescent layer is applied between the two electrodes to emit light, and the color of the emitted light is exposed on the surface of the substrate on the transparent electrode side. This is to display a pattern.

By the way, the above insulating layer contains Y2 oa and Aβ203.
．． A material having a relatively high dielectric strength, such as 5iOz, Si:+N4, or Taz Os, is used, and electron beam evaporation, sputtering, or the like has conventionally been widely used as a forming method. Furthermore, since the driving voltage of the EL element can be lowered as the thickness between the opposing electrodes is smaller, it is said that it is desirable to reduce the thickness of the insulating layer as well (unspecified literature).

[Problem to be solved by the invention]

However, insulating layers formed by electron beam evaporation or sputtering have poor density and have many defects such as bottle balls in the layer, and these defects are likely to cause dielectric breakdown of the device. The film thickness cannot be made thinner, and a film thickness of 3,000 angstroms or more is generally required, and the film thickness is usually about 4.000 to 5,000 angstroms.

Therefore, the conventional El-element has the problem of requiring a high driving voltage.

The present invention has been made to solve the above-mentioned problems, and aims to provide a method for manufacturing an EL element that has a low driving voltage, a long life, and has excellent light emitting characteristics.

[Means for Solving the Problems] As a result of intensive studies to achieve the above object, the inventors found that silicon nitride thin films formed by plasma CVD using a specific source gas are extremely It becomes a dense and highly insulating film, and when this silicon nitride thin film forms at least a part of the insulating layer of an El-element, the driving voltage is significantly reduced compared to conventional ones, and it can be used continuously for a long time. An EL element that does not easily cause dielectric breakdown even when used, has a long life without propagating dielectric breakdown even under harsh conditions, and has excellent luminous properties with a large increase in luminance as the voltage increases. They discovered that it can be obtained and came up with this invention.

That is, the present invention provides a method for manufacturing an EL element in which a light emitter layer and an insulating layer are disposed between opposing electrodes, at least one of which is transparent. Thickness formed by 2,0
Consisting of a silicon nitride thin film with a thickness of 00 Å or less,
A method for manufacturing an EL element characterized in that silane gas diluted with hydrogen gas and ammonia gas are used as source gases in this plasma CVD method at a ratio such that the flow rate ratio (volume) of ammonia gas/silane gas is 5 or more. .

[Structure and operation of the invention]

As is well known, the CVD method is a chemical vapor deposition method that is used to form various thin films, including in the semiconductor field.
Mical Vaper Deposition
) is a method in which two or more gasified components are introduced into a high vacuum chamber and reacted on a substrate to grow a thin film of the desired compound. The plasma CVD method used to form the insulating layer of the EL element in the present invention is a method in which a source gas is turned into plasma by high-frequency discharge, and the thin film is formed by a reaction between the plasmas. Note that the CVD method includes, in addition to the plasma CVD method, an optical CVD method that uses light energy to excite the reaction, a thermal CVD method that heats the substrate to a high temperature, and the like.

In this invention, the thickness 2 is formed by plasma CVD method.
At least a part of the insulating layer is made of a silicon nitride thin film of .
SiH4) gas and ammonia (NH3) gas are used, and the flow rate ratio of ammonia gas/silane gas is set to 5 or more.

That is, since the silicon nitride thin film formed by the plasma CVD method under the above conditions is extremely dense and has high insulating properties, the E
The L element is, for example, an EL formed by the method of Example 1 described later.
As is clear from the comparison between the curve A in FIG. 3 showing the brightness-voltage characteristics of the device and the curve in the same figure showing the same characteristics of the EL device obtained by the method of Comparative Example 3, it is clear that the electron beam evaporation method and sputtering method Compared to an EL element obtained by the conventional method of forming an insulating layer using a method, the emission start voltage is significantly lower, and the rise of luminance with respect to voltage is steeper, as shown by curve A1. In other words, since the luminance increases greatly with the increase in voltage, the driving voltage required to obtain the luminance that is actually used is much lower than that in the conventional method. Furthermore, because this low driving voltage also reduces the voltage applied to the insulating layer, and the insulating layer itself is extremely dense and has very few defects, the EL device produced by the method of this invention can be used continuously for long periods of time under normal conditions. Furthermore, even if a local breakdown occurs when used under harsh conditions of high voltage to obtain high brightness, the breakdown does not propagate to the surrounding area and remains a self-repairing breakdown, so it has excellent durability. It has an excellent long life.

On the other hand, when forming a silicon nitride thin film by the plasma CVD method, if the silane gas is diluted with an inert gas such as argon, or if the flow rate ratio of ammonia gas/silane gas is made smaller than 5, the curve F/ AB and C
The luminance of the EL element obtained by the method of Comparative Examples 1 and 2 shown in -
As shown in the voltage characteristics, the emission starting voltage is lower, but the increase in brightness with the increase in voltage is small, so the practical driving voltage is considerably higher than that of the EL element produced by the method of this invention, and when used continuously for a long period of time, Easily causes dielectric breakdown,
Moreover, this destruction becomes a propagation type that leads to destruction of the entire element.

As mentioned above, the reason why the EL element according to the method of this invention can be driven at a low voltage and has a long life is not clear, but
In general, compared to electron beam evaporation or sputtering, the CVD method itself avoids the occurrence of defects in the grown film due to high-energy particles and the contamination of impurities due to this, making it easier to form dense thin films. In the plasma CVD method for forming silicon thin films, silane gas is diluted with hydrogen gas, so the bonding force between silicon atoms in the gas phase is sealed by hydrogen, and the silicon component is dispersed even microscopically in the atmosphere. Si3N exists in an ideal uniformly dispersed state without being unevenly distributed, and as a result, an extremely dense thin film is formed, and the film composition has a high dielectric strength voltage due to the high concentration of ammonia relative to silane.

Because of the excellent density and insulation properties of this silicon nitride thin film, the thin film can be made as thin as 2,000 Å or less, which significantly reduces the driving voltage. It is assumed that this will lead to a longer life.

The amount of dilution of silane gas with hydrogen gas used in the above plasma CVD method is the total amount of diluted gas (S
It is preferable that the amount of silane gas in the i Ha 10 Hz ranges from 2 to 20% by volume, particularly preferably from 5 to 15% by volume. Further, the flow rate ratio (volume) of ammonia gas/silane gas is 5 or more as described above, but preferably 6
It is best to set it to 8. When this flow rate ratio becomes smaller than 5, the nitrogen component in the silicon nitride thin film becomes insufficient and its insulating properties become insufficient.

The conditions for the plasma CVD method are as follows: the atmosphere in the chamber has a degree of vacuum of about 0.5 to 1.5 Torr, the output of the high frequency power source for plasma generation is about 25 to 150 W, and the substrate temperature is about 200 to 350°C. Good.

The insulating film of the EL element formed by the method of the present invention is not only composed entirely of a silicon nitride thin film with a thickness of 2,000 Å or less formed by the plasma CVD method described above, but also a combination of this silicon nitride thin film and other insulating films. There is no problem even if it is composed of a composite membrane.

As the other insulating film in the case of forming the above composite film, various materials conventionally used for insulating layers of EL elements can be used, but in particular, strong materials with a dielectric constant of 100 or more such as PbTiO3, 5rTi○3, and TiO□ are used. It is preferable to use a dielectric material. That is, such ferroelectric materials are Al103, Y
203 has a higher dielectric property than SiO2, etc., so it is possible to lower the driving voltage of an EL element using it as an insulating layer, but it has the disadvantage of poor dielectric breakdown resistance. Even if the silicon nitride thin film is thin, sufficient dielectric breakdown resistance can be obtained due to its high insulation properties. Therefore, in this composite film, the thickness of the silicon nitride thin film can be made very thin, on the order of 200 to 1,000 layers, thereby reducing the driving voltage.

The insulating film made of the above-mentioned ferroelectric material can be formed by electron beam evaporation, sputtering, or various CVD methods.
Any existing thin film forming means such as the D method can be employed. The thickness of the film is preferably about 3,000 to 6,000 people.

On the other hand, when the insulating layer is formed using only a silicon nitride thin film by the above-mentioned CVD method, the thickness is preferably 500 Å.
As mentioned above, it is best to set the number to 1,000 to 2,000 people.

FIGS. 1 and 2 show an example of the structure of a double insulation type EL element obtained by the method of the present invention.

In both figures, ■ is a substrate made of a translucent material such as glass, and on this is a 1,000 mm thick film made of indium-tin composite oxide (hereinafter referred to as IT○), etc.
~3,000 people display side transparent electrode 2, first insulating layer 3, light emitter layer 4, second insulating layer 5, Aj2 thin film and IT
Patterned into a desired shape made of O film with a thickness of 500~
Approximately 3,000 back electrodes 6 are provided.

In the EL device shown in FIG. 1, both the first and second insulating layers 3.5 are made of silicon nitride thin films with a thickness of 2,000 Å or less formed by the plasma CVD method described above. Further, in the E L element shown in FIG. 2, the second insulating layer 5
is composed of the same silicon nitride thin film as above, but
The first insulating layer 3 is composed of a composite film of an insulating film 3a on the substrate side made of the above-mentioned ferroelectric material and an insulating film 3b on the light emitting layer side made of the same silicon nitride thin film as described above.

As the constituent material of the luminescent layer 4, any of the various luminescent materials known for use in EL devices can be used, and usually a base material such as ZnS mixed with a small amount of a luminescence activator, such as ZnS, is used. :TbF3 (green emission), Z
nS: SmF3 (red emission), ZnS:M
n (yellow-orange emission), ZnS:TmF3 (blue emission)
, ZnS:PrFa (white light emission), ZnS:DyF
3 (yellow emission) and the like are preferably used. Such a light emitting layer 4 is formed by forming the first insulating layer 3 by various thin film forming methods including electron beam evaporation and sputtering.
It will be installed on the top with a thickness of about 3,000 to 6,000 people.

In the EL device shown in FIG. 2, the first insulating layer 3 is a composite film of an insulating film made of silicon nitride thin IFJ produced by the plasma CVD method and an insulating film made of ferroelectric material. The insulating layer 5 may be a similar composite film, or both the insulating layers 3 and 5 may be a similar composite film.

Further, in these composite films, an insulating film made of a silicon nitride thin film may be disposed on either the light emitting layer 4 side or the opposite side.

Further, the method of the present invention can be applied to a double insulation type EL as shown in the figure.
In addition to devices, there are also table-insulated EL devices, EL devices with a multilayer structure with two or more light-emitting layers, and E with multiple electrode layers in which one electrode facing each other is laminated with an insulating layer interposed between them.
It is applicable to manufacturing various EL elements such as L elements.

[Effects of the Invention] According to the method of the invention, at least a part of the insulating layer interposed between the facing electrode and the light emitting layer is formed by plasma CVD under specific conditions to a thickness of 2°,000 Å or less. Due to the excellent density and insulation properties of this silicon nitride thin film, as well as its thin film thickness, the driving voltage is extremely low, and it has a long lifespan that is unlikely to cause dielectric breakdown even with continuous use. It is possible to obtain an EL element of.

〔Example〕

The present invention will be specifically described below based on examples.

Example 1 Thickness 1. A 2 mm thick ITO film was deposited on one surface of a 1 mm alkali-free glass substrate by sputtering.
After forming a transparent electrode with a thickness of 1,000 μm, a first insulating layer made of a silicon nitride thin film with a thickness of 1,500 μm was formed on the transparent electrode using a plasma CVD method, and a first insulating layer with a thickness of 1,500 μm was formed on this transparent electrode using an electron beam evaporation method. A 5,000-layer thick phosphor layer made of Zns:TbF is formed, and a second 1,500-layer phosphor layer is formed on this phosphor layer by plasma CVD.
Finally, on the second insulating layer, a back electrode consisting of a 2,000-thick AN thin film was formed by resistance heating evaporation, and the F and L elements A1 having the structure shown in FIG. 1 were formed. was created.

Note that plasma CV for forming the first and second insulating layers
For both method D, the vacuum degree is I Torr, the board temperature is 250°C, the high frequency (13,56 Mllz) output is 100
In W, SiH4 gas diluted to a concentration of 10% by volume with H2 gas and NH3 gas are used as source gases.
The flow rate ratio of Hs gas/S i H4 gas was 7, the total supply rate was 80 mA/min, and the film growth rate was 100 people/min.

Comparative Example 1 The first and second insulating layers were formed using SiH4 as a source gas.
Gas diluted with Ar gas to a concentration of 10% by volume and NH
Example 1 except that the silicon nitride thin film was formed by the plasma CVD method under the same conditions as Example 1, using 3 gases at a flow rate ratio of NH3 gas/S I Ha gas of 7. EL element B was produced in the same manner as above.

Comparative Example 2 The first and second insulating layers were formed using SiH4 as a source gas.
Gas diluted with H2 gas to a concentration of 10% by volume and N
H3 gas and N H3 gas/SiH.

EL was carried out in the same manner as in Example 1, except that the gas flow rate ratio was 1 and the silicon nitride thin film was formed by plasma CVD under the same conditions as in Example 1.
Element C was produced.

Comparative Example 3 The first and second insulating layers were both Y2O3 films with a thickness of 4,000 yen formed by electron beam evaporation.
An EL device was produced in the same manner as in Example 1.

Example 2 The first insulating layer was a substrate-side insulating film made of a 5,000-thick PbTiO2 (dielectric constant: 100) film formed by high-frequency sputtering and plasma CVD under the same conditions as in Example 1. Except for the composite film with the insulating film on the light emitting layer side, which was made of a silicon nitride thin film with a thickness of 500 μm.
EL element A2 having the structure shown in FIG. 2 in the same manner as in Example 1
was created.

EL element AI- obtained in the above Examples and Comparative Examples
For D, 5 KHz between the transparent electrode and the back electrode
The brightness-voltage characteristics were investigated by applying an alternating current pulse voltage of 100 mL and gradually increasing this voltage. The results are shown in FIG. Note that the symbol of each curve in the figure corresponds to the symbol A, -D of each EL element.

In addition, for each EL element, the dielectric constant of the first insulating layer, the dielectric breakdown field strength, the dielectric loss, and the time until dielectric breakdown occurs when continuously driven by applying an AC pulse voltage of 5Kilz-150V are shown. Durability was measured for each. These results are shown in the table below along with the emission start voltage and the drive voltage at which practical brightness (approximately 100 Cd/+yf) was obtained when the above voltage was applied.

In addition, in the above table, in the durability section, E L according to Comparative Examples 1 to 3
The fractures that occurred in elements B-D are all propagation type fractures,
After its destruction, it was no longer possible to display it for practical purposes. In addition, Example 1
．． For EL elements A+ and A2 according to 2, an additional 5KH
When observed after 1,000 hours of continuous operation by applying an alternating current pulse voltage of 140 V and 140 V, slight local destruction occurred in both cases, but these destruction areas did not propagate to the surrounding area and were not a practical problem. It was confirmed that the damage remained in a self-repairing type of failure.

As is clear from the results shown in the table above and FIG. 3, EL element A obtained by the method of the present invention in which at least a part of the insulating layer is made of a silicon nitride thin film formed by plasma CVD under specific conditions; , A2 has a luminescence starting voltage of approximately 50 V for EL element A1, compared to an EL element in which an insulating layer is formed using a conventional general-purpose electron beam evaporation method;
The driving voltage to obtain practical brightness is approximately 70V for EL element A1 and approximately 90V for EL element A2.
Moreover, even after long-term continuous use, no dielectric breakdown occurs and the lifespan is extremely long. On the other hand, even if the insulating layer is a silicon nitride thin film formed by the plasma CVD method, the element is obtained using a gas in which the silane gas as a reaction component is diluted with a gas other than hydrogen gas (EL). In the device B) and the device obtained using a source gas with a too small flow rate ratio of silane gas/ammonia gas (EL device C), the emission start voltage is low, but the driving voltage is lower than that of the EL device AI according to the method of this invention. It is found that it is considerably more expensive than A2 and also has a shorter lifespan.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing structural examples of electroluminescent devices obtained by the method of the present invention, and FIG. 3 shows the luminance of electroluminescent devices obtained by the methods of Examples and Comparative Examples of the present invention. - It is a voltage characteristic diagram. (V)

Claims (1)

[Claims] (1) In a method for manufacturing an electroluminescent display element in which a light emitter layer and an insulating layer are disposed between opposing electrodes, at least one of which is transparent, at least a portion of the insulating layer is formed by plasma CVD. It is composed of a silicon nitride thin film formed with a thickness of 2,000 Å or less, and silane gas diluted with hydrogen gas and ammonia gas are used as source gases in this plasma CVD method, and the flow rate ratio (volume) of ammonia gas/silane gas is 5. A method for manufacturing an electroluminescent element, characterized in that the electroluminescent element is used in the above ratio.