JPH01213991A - Transparent electrode substrate and electroluminescence element utilizing same - Google Patents

Abstract

PURPOSE:To obtain improved dielectric strength and luminous efficiency without making electric resistance higher, by using an SnO2:F film as a transparent electrode. CONSTITUTION:A stannic oxide film containing fluorine, i.e. an SnO2:F film, used as a transparent electrode 2 on a transparent electrode substrate 1 performs its electric conduction function owing to the presence of the fluorine as a impurity in the stannic oxide. Its electric resistance, therefore, does not change if it is subjected to oxidation or reduction. When the transparent electrode substrate 1 having such a transparent electrode 2 is thus used as a display-side substrate of a EL-element, the electric resistance of the electrode film does not become higher if the transparent electrode 2 is subjected to sputtering in an atmosphere containing oxygen for forming an insulting oxide layer thereon or subjected to annealing after the film formation, so that an electroluminescence(EL) element with high dielectric strength and high luminous efficiency 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 emitting layer and an insulating layer adjacent thereto are arranged, and the insulating layer is provided on only one side of the light emitting layer, such as the table insulation type, and the double insulation type, where the insulating layer is provided on both sides. There are some known devices in which the luminescent layer is not limited to one layer, but two or more layers are laminated with an insulating layer interposed therebetween.

In the AC driving method, such an EL element is driven by applying an AC voltage between both electrodes to apply an electric field equal to or higher than a threshold electric field for starting light emission to the luminescent layer, causing it to emit light, and changing the color of the emitted light. A predetermined pattern is displayed by exposing the surface of the substrate on the transparent electrode side.

Generally, the insulating layer is made of PbTiOs, BaTiO3, Y203, A1) formed by various vacuum thin film forming methods including sputtering.
Thin films made of insulating materials such as zOx, Slo2, Taxo, Si3N4 are used. In addition, the transparent electrode on the display side is covered with a transparent conductive film made of a composite oxide containing indium and a small amount of tin (hereinafter referred to as ITO film), and the electrode on the back side opposite to this is made of the above-mentioned ITO film or opaque. AI membranes are used for each (document unknown)
.

[Problem to be solved by the invention]

However, when forming an insulating layer made of an oxide by sputtering on a transparent electrode made of an ITO film in the production of an EL element, it is generally made of a mixed gas of an inert gas such as argon gas and oxygen gas. Since sputtering is performed with the substrate temperature set at a high temperature in an oxygen-containing atmosphere, there is a problem that the ITO film is oxidized and becomes highly resistive.

For example, a mixed gas of argon gas and oxygen gas (Ar
10x = 90/10) at a substrate temperature of 600°C.
b When T i Os is sputtered, ITon!
The electrical resistance increases by about 20 times. Further, when annealing treatment is performed in the atmosphere at, for example, about 400° C., which is usually performed after the formation of the oxide insulating layer, the electrical resistance of the ITO film further increases significantly.

Such an increase in the electrical resistance of the ITO film causes a decrease in the dielectric breakdown voltage, that is, a dielectric breakdown voltage, and a decrease in the luminous efficiency of the EL device, and is a major problem in improving the device performance.

Note that as a means to alleviate the high resistance of the ITO film as described above, it is possible to use a sputtering gas that does not contain oxygen gas or to lower the substrate temperature during sputtering to form the oxide insulating layer. However, these methods cause compositional changes and deterioration of the density of the formed oxide insulating layer, making it impossible to obtain sufficient properties as an insulating layer.

In light of the above-mentioned circumstances, the present invention provides a transparent electrode substrate whose electrical resistance does not increase even after high-temperature heat treatment in an oxygen-containing atmosphere, and an oxide thin film in which an insulating layer is formed by sputtering using the substrate. The object of the present invention is to provide an EL element that exhibits high dielectric strength and luminous efficiency even in certain cases.

[Means to solve the problem]

As a result of intensive studies to achieve the above object, the inventors found that when a transparent electrode formed on one side of a transparent substrate is made of a specific transparent conductive material, The electrical resistance of the electrode does not increase even after high-temperature heat treatment. Therefore, in an EL device using this transparent electrode substrate, the oxide insulating layer in contact with the transparent electrode is formed by sputtering or annealed in air. The present inventors have discovered that high dielectric strength and luminous efficiency can be obtained even with a high dielectric strength, and have thus come to form this invention.

That is, the first aspect of the present invention relates to a transparent electrode substrate in which a transparent electrode made of a thin film of tin oxide containing fluorine is formed on one side of a transparent substrate. The second aspect of the present invention is to provide an oxide insulator in contact with the transparent electrode between a transparent electrode made of a fluorine-containing tin oxide thin film formed on one side of the transparent substrate and a back electrode opposing the transparent electrode. The present invention relates to an EL element including a layer and a light emitting layer.

[Structure and operation of the invention]

The fluorine-containing tin oxide thin film (hereinafter referred to as 5nOt:F film) used for the transparent electrode in the transparent electrode substrate of this invention exhibits its conductive function due to the presence of fluorine as an impurity in the tin oxide. Therefore, even when subjected to oxidation or reduction, no change in electrical resistance occurs. Therefore, when a transparent electrode substrate having such a transparent electrode is used as a display side substrate of an EL element, an oxide insulating layer is formed on the transparent electrode by sputtering in an oxygen-containing atmosphere, or Even if annealing treatment is performed in air afterwards, the resistance of the electrode film does not increase, and an EL element exhibiting high dielectric strength and luminous efficiency can be obtained.

In contrast, I
The conductivity of a TO film is based on the presence of oxygen vacancies in the film, so when it is oxidized, oxygen is supplied to the oxygen vacancies and the conductivity is impaired. In particular, in a sputtering method in an oxygen-containing atmosphere, oxygen is turned into plasma and is in an extremely active state, which tends to cause an oxidation reaction, resulting in a significantly high resistance in an ITo film. Note that thin films made of tin oxide alone are also known as transparent electrodes, but
Since the conductivity of this tin oxide film is also based on oxygen vacancies similar to those of the ITO film, the resistance increases due to oxidation as described above.

The SnO2:F film used in this invention preferably has a fluorine to tin atomic ratio F/Sn of about 1/1 to 9/1; if the fluorine ratio is too small, sufficient conductivity may not be obtained. On the other hand, if the above ratio is too high, there is a problem that the light transmittance in the visible range decreases, and the film formation itself becomes difficult. In addition, the thickness of the Sn0,:F film varies depending on the application, but in general, the thickness is 1,000 to 5,000, and the thickness of the E
For an electrode film such as an L element, it is preferable to change color by about 1,500 to 3,000.

The means for forming such a SnO□:F film is not particularly limited, and various methods can be adopted, but CVD
The cal vapor deposition method is most preferred.

The EL element of the present invention uses the above-mentioned transparent electrode substrate on which the SnO,:F film is formed as a substrate having a transparent electrode on the display side, and a transparent A double insulation type EL element has an oxide insulating layer and a light emitter layer in contact with the electrode, and has an insulating layer between the light emitter layer and the back electrode as well as the above insulating layer, and a double insulation type EL element that has an insulating layer on the light emitter layer. It includes a desk-insulated EL element in which a back electrode is directly formed.

FIG. 1 shows an example of the structure of a double insulation type EL element to which the present invention is applied.

In the figure, l is a substrate made of a transparent material such as glass, 2 is a transparent electrode on the display side made of the SnO□:F film, 3 is the first insulating layer on the display side, and 4 is a luminescent layer. , 5 is a second insulating layer on the back side, and 6 is a back electrode.

The first insulating layer 3 is made of oxide and has a thickness of 3.0 mm as described above.
000 to 6,000 people, and its formation methods include sputtering method, vacuum evaporation method, CVD method,
Although it is possible to employ various existing methods of forming thin films in vacuum, such as ion blasting, the application effect of the present invention is limited when a method of forming a film in an oxygen-containing atmosphere, especially a sputtering method in such an atmosphere, is adopted. big. As the oxide constituting the first insulating layer 3, for example, PbTiO3
, Ta2o3, BaTi0i, YzOs, Alz
Examples include O3, SiO□, and the like.

Further, the second insulating layer 5 is made of an oxide similar to the above or S
It is made of an insulating material other than oxide, such as i3N, and is formed to a thickness of about 1,000 to 6,000 with discoloration by the various vacuum thin film forming methods 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. Usually, a base material such as ZnS is mixed with a small amount of a luminescence activator, such as ZnS. nS: T bF3 (green emission)
, ZnS: Sml”, (red emission), ZnS
:Mn (yellow-orange light emission), ZnS:TmFz (blue light emission)
, ZnS:PrF3 (white light emission), ZnS:DyF=(
(yellow emission) etc. are preferably used.

Such a light emitter layer 4 is formed to a thickness of about 3,000 to 3,000 seconds by various thin film forming methods similar to those for the above-mentioned insulating layer 5.

The back electrode 6 is made of an Al film, the SnO, :F film, or I
It is made of a TO film or the like, and is formed to a thickness of about 1,000 to 3,000 with discoloration using the various thin film forming methods described above.

In the EL element having the above configuration, a voltage that can apply an electric field exceeding the luminescence initiation threshold electric field to the luminescent layer 4 is applied to the picture electrode 2.
6, the light emitting layer 4 emits light, and this light emission is visually recognized through the substrate 1. At this time, even if the first insulating layer 3 is formed by a sputtering method in an oxygen-containing atmosphere, or even if an annealing treatment is performed after the formation of the insulating layer 3, the electrical resistance of the transparent electrode 2 Since it has a small value and excellent conductivity, high dielectric strength voltage and luminous efficiency can be obtained.

Note that the present invention is applicable to EL devices having multiple insulating layers between a transparent electrode and a light-emitting layer, and EL devices in which a plurality of light-emitting layers are stacked with an insulating layer interposed between them. Applicable to In addition, in the insulating layer at a position not in contact with the display-side transparent electrode in these EL elements, the second
Similarly to the insulating layer 5, insulating materials other than oxides can also be used.

〔Effect of the invention〕

The transparent electrode substrate according to the present invention uses SnO as the transparent electrode.
, :F film is used, so even if heat treated in an oxygen-containing atmosphere, the transparent electrode does not have high resistance unlike conventional general-purpose ITO films, and exhibits stable and excellent conductivity. do.

Furthermore, since the EL element according to the present invention uses the transparent electrode substrate described above on the display side, the oxide insulating layer in contact with the transparent electrode is formed by sputtering in an oxygen-containing atmosphere. Even when the film is annealed in air after film formation, it exhibits superior dielectric strength and luminous efficiency compared to EL elements with conventional configurations.

〔Example〕

Hereinafter, this invention will be specifically explained based on examples.

Example 1 A 2,000-thick SnO:F film (F/Sn atomic ratio 6/4) was deposited on one side of the entire surface of a transparent substrate made of a glass plate with a thickness of 1.1) 1. A transparent electrode was formed on the display side.

Next, a first insulating layer made of PbTi0z with a thickness of s and ooo is deposited on the transparent electrode by high-frequency sputtering using a mixed gas of argon gas and oxygen gas (volume ratio of Ar:02=90: 10) at a vacuum level of 2 x 10-'Torr and a substrate temperature of 640°C.
, formed at a deposition rate of 80 people/min, and then sequentially deposited on this insulating layer a phosphor layer of ZnS:TbF with a thickness of 5,000 people by electron beam evaporation, and plasma CVD.
A second layer made of silicon nitride with a thickness of 1.000 mm by the D method.
Insulating layer, 1,500 mm thick by resistance heating evaporation method
A back electrode consisting of a film is formed, and an E of the configuration shown in FIG.
An L element A1 was produced.

Note that the sheet resistance of the transparent electrode before and after the formation of the first insulating layer was both 20Ω/hole, and there was no change. In addition to the above, after forming the first insulating layer,
The sheet resistance of the transparent electrode was measured after annealing for 1 hour at , but it remained unchanged at 20Ω/hole.

Comparative Example 1 Same as Example 1 except that instead of the 5nO□:F film, a substrate having a transparent electrode made of a 2,000-layer ITO film formed by EB (electron beam) evaporation was used. An EL element A2 was produced.

In this case, the sheet resistance of the transparent electrode was 1097 before the formation of the first insulating layer, but after the same formation, the sheet resistance was 40 times as high as 40.
The resistance increased significantly to 0Ω/hole, and after the same annealing treatment as in Example 1, it became 300Ω/hole.

Example 2 Taxes with a thickness of 4,000 were placed on a transparent electrode made of a SnO:F film formed on a substrate in the same manner as in Example 1.
A mixed gas of argon gas and oxygen gas (volume ratio of Ar:0□=80
:20), by high frequency sputtering method under the conditions of a vacuum degree of 2 x 10-'' Torr, a substrate temperature of 300°C, and a film formation rate of 60 people/min. The light emitter layer and the first insulating layer are formed to a thickness of 4,000 mm using the same high frequency sputtering method.
A second insulating layer made of O, and a back electrode similar to that in Example 1 were formed to produce an EL element B1 having the configuration shown in FIG. In this case, as in Example 1, the resistance of the transparent electrode remained unchanged at 20Ω/hole before and after the formation of the first insulating layer.

Comparative Example 2 EL element B2 was produced in the same manner as in Example 2, except that instead of the SnOz:F film, a substrate having a transparent electrode made of a 2,000-thick ITO film formed by the EI3 vapor deposition method was used. was created. In this case, the sheet resistance of the transparent electrode is the first
Before the formation of the insulating layer, the resistance was 10 Ω/hole, but after the same formation, it increased significantly to 300 Ω/hole, which is 30 times as large.

EL element A1 of the above example and comparative example. B1, A2
．． Regarding B2, when the brightness-voltage characteristics were measured by applying an AC sinusoidal voltage of 5KIIz, the results shown in FIG. 2 were obtained. Note that the symbol of each curve in the figure corresponds to the symbol of the EL element.

Comparison of curves AI and A2 in Figure 2 and curves B1 and 82
As is clear from the comparison, the EL element of the present invention (Al
, Bl) have a significantly higher dielectric breakdown voltage and increased maximum brightness compared to the conventionally configured EL elements (A2, B2) that use an ITO film as the transparent electrode on the display side, and have improved dielectric breakdown voltage and luminous efficiency. It turns out that it is excellent.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a structural example of an electroluminescent device according to the present invention, and FIG. 2 is a brightness-voltage characteristic diagram of electroluminescent devices according to an example of the present invention and a comparative example. 1... Transparent substrate, 2... Transparent electrode, 3... First
insulating layer (oxide insulating layer), 4... luminescent layer, 5...
・Second insulating layer (back side insulating layer) 6...Back electrode patent applicant Hitachi Maxell, Ltd.

Claims (6)

[Claims] (1) A transparent electrode substrate in which a transparent electrode made of a thin film of tin oxide containing fluorine is formed on one side of a transparent substrate. (2) The atomic ratio F/Sn of fluorine and tin in the transparent electrode is 1
The transparent electrode substrate according to claim 1, which is in the range of /1 to 9/1. (3) The transparent electrode substrate according to claim (1) or (2), wherein the transparent electrode has a thickness of 1,000 to 5,000 Å. (4) An oxide insulating layer and a luminescent layer in contact with the transparent electrode are provided between the transparent electrode made of a thin film of tin oxide containing fluorine formed on one side of the transparent substrate and the back electrode facing the transparent electrode. An electroluminescent element that is equipped with. (5) The electroluminescent device according to claim (4), wherein the oxide insulating layer in contact with the transparent electrode is formed by sputtering in an oxygen-containing atmosphere. (6) The electroluminescence device according to claim (4) or (5), wherein a back side insulating layer is interposed between the light emitter layer and the back electrode.