JPH02148598A - Electroluminescence device - Google Patents

Abstract

PURPOSE:To perform stable luminous display of high luminance by providing a niobium oxide layer between an electrode and a dielectric layer, and by constructing specified two-layered structure composed of a semi-insulating thin film layer and an insulating thin film, for the dielectric layer adjoining the niobium oxide layer. CONSTITUTION:On a substrate 1, an electrode 2 on the side of display, a first dielectric layer 3, a luminous layer 4, a second dielectric layer 5 that is composed of an insulating thin film layer 5a and a semi-insulating thin film layer 5b, a niobium oxide layer 6, and a back plate 7 are formed. Since the niobium oxide layer 6 works as a low resistance layer and virtually reduces the potential barrier between the electrode 7 and the dielectric layer 5 through itself, the injection of electric charge from the electrode 7 to the dielectric layer 5 is increased. Also, since the dielectric layer 5 adjoining the layer 6 is of two- layered structure, electric charge is injected in the layer 5b, and most of moves in the layer 5b and is accumulated in the interface with the layer 5a, however, the amount of electric charge injection being large, a part of high energy electric charge, which accordingly exists in a large number, is injected in the layer 5a so as to become an effective carrier that contributes to luminescence.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a Nilecoluminescence device (hereinafter referred to as E L ) used in display devices, etc., in particular, a dielectric layer on both sides of a light emitting layer. The present invention relates to a double insulation type EL element having the following characteristics.

[Conventional technology]

This type of double-insulated EL device has a structure in which a light-emitting layer and a dielectric layer sandwiching the light-emitting layer from both sides are arranged between a pair of electrodes that are transparent at least on the display side and usually one of which is patterned. have. In the AC driving method, this element is driven by applying an AC voltage between both electrodes to apply an electric field to the light-emitting layer that is equal to or greater than the threshold electric field for starting light emission, causing the light-emitting layer to emit light. A predetermined pattern is displayed on the surface of the screen.

By the way, in order to improve the display performance of such EL elements, it is necessary to increase the luminance of the emitted light, and as a means of achieving this, conventional attempts have been made to increase the luminance by increasing the amount of charge injected into the luminescent layer (for example, "Appl.・phys-Let
T, J7, 1979, “Electronic JM IEICE Journal J1.984
April issue, etc.) have been published. On the other hand, the inventors previously discovered that niobium oxide (NbzOs) was used between the electrode and the dielectric layer.
It is proposed to increase the brightness and reduce the driving voltage by interposing a layer (Japanese Patent Application No. 61-243881).
issue).

(Problems to be Solved by the Invention) However, although the above-mentioned means of simply increasing the amount of charge injection increases the brightness, it also lowers the luminous efficiency and deteriorates the stability of the device, resulting in display problems due to local breakdown. There was a problem that quality deterioration and life shortening were likely to occur.

On the other hand, in the method of interposing the niobium oxide layer, the niobium oxide layer acts as a low-resistance layer, increases the charge injection rate from the electrode, and has the function of preventing the generation of leakage current that causes local breakdown. It has been confirmed that this increases the brightness, lowers the driving voltage, and improves the stability of the device, resulting in a longer life.

However, even with the above-mentioned EL device with a niobium oxide layer interposed, it is still not sufficient, especially in terms of luminous efficiency, and there is still room for improvement. It is hoped that

The present invention was made in order to meet the above-mentioned needs, and an object of the present invention is to provide a high-performance EL element that can exhibit high luminance and high luminous efficiency.

[Means to solve the problem]

As a result of intensive studies to achieve the above object, the inventors discovered that in a structure in which a niobium oxide layer is interposed between an electrode and a dielectric layer as proposed above, the niobium oxide layer is We discovered that when the dielectric layer has a specific two-layer structure, the high-energy charge density that contributes to light emission increases when a voltage is applied, and that this makes it possible to realize an EL device that can obtain high-luminance light with high luminous efficiency. He came up with an invention.

That is, the present invention provides a double insulation type EL element in which a light emitting layer and a dielectric layer sandwiching the light emitting layer from both sides are arranged between opposing electrodes, at least one of which is transparent. A niobium oxide layer is formed between the niobium oxide layer and the light emitting layer, and a dielectric layer located between the niobium oxide layer and the light emitting layer is a semi-insulating thin film layer in contact with the niobium oxide layer (1! layer and an insulating thin film layer in contact with the light emitting layer). This relates to an EL element characterized by having a two-layer structure.

Further, in the present invention, in the above EL element, the semi-insulating thin film layer is made of YzOs, Taxo3, Sm, O+,
BaTi0. , BaTa, and Oa, and the insulating thin film layer is formed by electron beam evaporation, sputtering, and CVD (Che+w
Sin formed by any of the chemical vapor deposition (chemical vapor deposition) methods.
2 N4, AI! z Oz , A I NSS
A configuration consisting of a type of thin film selected from IA I ON is designated as preferred type B.

[Structure and operation of the invention]

In the EL element of the present invention, the niobium oxide layer interposed between the electrode and the dielectric layer acts as a low resistance layer that normally has a specific resistance of about 1×10 sΩ・am, and the electrode and dielectric layer are interposed between the electrode and the dielectric layer. Substantially lowering the potential barrier between the layers results in an increased amount of charge injection from the electrodes into the dielectric layer when a voltage is applied between opposing electrodes.

Furthermore, since the dielectric layer adjacent to this niobium oxide layer has a two-layer structure as described above, the above charge is injected into the semi-insulating thin film layer of the dielectric layer, and this injected charge is induced by the electric field. Most of the charge moves within the semi-insulating thin film layer and accumulates at the interface with the insulating thin film layer, but as mentioned above, the large amount of charge injection causes a large amount of charge (some of the existing high-energy state charges It becomes an effective carrier that is injected into the insulating thin film layer and contributes to light emission.

Therefore, the EL element of the present invention has a much higher density of high-energy effective carriers during driving than conventional EL elements, and achieves high luminance light emission with high luminous efficiency.

The thickness of the above-mentioned niobium oxide layer is preferably about 500 to 5,000. If it is too thin, the above function will not be fully exhibited, and if it is too thick, the unevenness of the film surface may increase. There is. Further, as the forming means, various existing thin film forming methods such as various vacuum evaporation methods including electron beam evaporation, sputtering method, and ion blating method can be employed.

As for the dielectric layer of the two-layer structure adjacent to this niobium oxide layer, the resistivity of the semi-insulating thin film layer on the niobium oxide layer side is 108~
It is preferable that the specific resistance of the insulating thin film layer on the light emitting layer side is about 1012 Ω·ω or more. Further, the dielectric material constituting both thin film layers is not particularly limited, but for the semi-insulating thin film layer, YzOz, Ta2os, etc. formed by electron beam evaporation method or sputtering method are used.
, Sm.

Oz, BaTi0t, BaTi0t, etc., 5iOz-, Slz formed by any of the electron beam evaporation method, sputtering method, and CVD method in the insulating thin film layer.
Suitable thin films include N4, All Owl, AIN, 5iA6ON, and the like.

Note that the thickness of both the above thin film layers is 2,
000~6,000 people, 500~ for insulating thin film layer
Approximately 2,000 people and the total thickness of the dielectric layer is 3,000
A range of approximately 0 to s, ooo people is recommended.

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, ■ is a substrate made of a transparent material such as a glass plate, and 2 is an indium-tin composite oxide film (hereinafter referred to as ITO).
The thickness is 1.000~
3,000 electrodes on the display side, 3 a first dielectric layer on the display side, 4 a light emitting layer, and 5 a two-layer structure consisting of the above-mentioned insulating thin film layer 5a and semi-insulating thin film layer 5b. The second dielectric layer 6 is the aforementioned niobium oxide layer, and 7 is an electrode on the back side having a thickness of approximately 1,000 to 3,000 layers and made of an ITO film, a /l film, or the like. Note that in this EL element, the second dielectric N5
The semi-insulating thin film layer 5b is formed so that each layer below it covers the peripheral side surface and also serves as a protective layer.

The constituent materials of the first dielectric layer 3 include Y2O2, Alz
Various semi-insulating and insulating dielectric materials conventionally used for the dielectric layer of this type of EL element, such as 03, SiO2, SizN4, and Ta2os, can be used. The dielectric layer 3 can be formed by various thin film forming methods such as electron beam evaporation, sputtering, ion blasting, and CVD.
Although the thickness is about 0.00 to 6.000 mm, it is possible to have a laminated structure of two or more layers made of different dielectric materials instead of a single layer structure.

As the constituent material of the light-emitting layer 4, any of the various light-emitting materials known for use in EL devices can be used. Usually, a small amount of light-emitting activator is added to a base material made of a phosphor such as ZnS, SrS, or CaS. Blends, such as ZnS:Tb
, F (green emission), Z n S : S m )
F (red emission), ZnS:Mn (yellow-orange emission), Z
nS; Tm, F (blue emission), ZnS: P
r + F (white light emission), ZnS: Dy.

F (yellow emission), CaS:Eu (red emission), Srs:
ce (blue-green light emission), SrS:Pr (white light emission), and the like. Such a light-emitting layer 4 can be formed using various thin film forming methods similar to those for the first dielectric layer 3 described above.
It is formed to a thickness of about 8,000 people.

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 2.7.
By applying a voltage between the two, the light emitting layer 4 emits light, and this light emission is visually recognized through the substrate 1 in a predetermined display pattern. At this time, due to the above-mentioned effects of the niobium oxide layer 6 and the second insulating layer 5 having a two-layer structure, stable display can be achieved by emitting light with extremely high luminous efficiency and high brightness. In addition, this EL element is resistant to dielectric breakdown even after long-term continuous operation.
It has a long lifespan.

In the illustrated structure example, the niobium oxide layer 6 is connected to the electrode 7 on the back side.
The second dielectric layer 5 has a two-layer structure consisting of insulating and semi-insulating thin film layers 5a and 5b, but in this invention, contrary to the above, the niobium oxide layer is provided in contact with the display side electrode. The first dielectric layer may have a two-layer structure similar to the above, or the first and second dielectric layers may have a two-layer structure similar to the above by providing a niobium oxide layer in contact with the electrodes on both sides. A layered structure may also be used.

Furthermore, the present invention provides a double insulation type EL element in which the light emitting layer has a multilayer structure of two or more layers, or in which the electrode on one side is composed of a plurality of electrode films laminated with an insulating layer interposed between them. is also included.

〔Effect of the invention〕

In the double insulation type EL element according to the present invention, a niobium oxide layer is interposed between at least one of the opposing electrodes and a dielectric layer, and the dielectric layer adjacent to the niobium oxide layer is semi-insulating. Since it has a specific two-layer structure consisting of a thin film layer and an insulating thin film layer, it can perform stable luminescent display with high brightness with extremely high luminous efficiency and has a long life. In particular, by forming the semi-insulating thin film layer and the insulating thin film layer in this element from the above-mentioned specific material (W film), the above-mentioned effects can be more prominently exhibited.

〔Example〕

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

Example 1 A substrate made of a 1.1 mm thick glass plate on which a display side electrode made of a 2,000-thick ITO film was formed in advance on one side was used. , 5,000 thick Ta2O by high frequency sputtering method
, a first dielectric layer consisting of 5,000 nm thick ZnS by electron beam evaporation; a light emitting layer consisting of Mn; 1,000 nm thick AlzO3 by high frequency sputtering.
The second dielectric layer has a two-layer structure, consisting of a lower insulating thin film layer formed by high-frequency sputtering and an upper semi-insulating thin film layer made of Ta, O, with a thickness of 3,000 yen by high-frequency sputtering, and an electron beam. A back side electrode having a predetermined pattern consisting of a niobium oxide layer with a thickness of 1,000 thick by vapor deposition and an Al film with a thickness of 1,500 thick by resistance heating vapor deposition was formed to form the structure shown in FIG. An EL element A1 was produced.

Comparative Example 1 EL element B1 was produced in the same manner as in Example 1 except that the niobium oxide layer was not formed.

Comparative Example 2 The second dielectric layer was formed by high frequency sputtering to a thickness of 5.
EL element B2 was produced in the same manner as in Example 1 except that the single layer was made of Ta of 0.000 and 0.05.

Comparative Example 3 EL was carried out in the same manner as in Example 1, except that the vertical relationship between the insulating thin film layer and the semi-insulating thin film layer in the second dielectric layer was reversed.
Element B3 was produced.

Example 2 The thickness of the first dielectric layer was 2.00 mm by plasma CVD method.
A layer consisting of 0.0 μm of St, N4, a thickness of 5.000 μm of Zns:Tb, a thickness of the light emitting layer by high frequency sputtering method, a layer of 5.000 μm of Zns:Tb, a thickness of the insulating thin film layer of the second dielectric layer by plasma CVD method. A BL element was fabricated in the same manner as in Example 1, except that a layer of 5iffN4 with a thickness of 1,000 and a layer of Y2O with a thickness of 3,000 by electron beam evaporation were formed as semi-insulating thin film layers. A2 was produced.

Comparative Example 4 EL element B4 was produced in the same manner as in Example 2 except that the niobium oxide layer was not formed.

Comparative Example 5 The second dielectric layer was formed with a thickness of 2°000 by plasma CVD method.
EL element B5 was produced in the same manner as in Example 1 except that a single layer consisting of human St and N4 was used.

Luminance-voltage characteristics and luminous efficiency by lK11z driving for the EL elements of the above examples and comparative examples, respectively.
The voltage characteristics were measured. The results are expressed as EL elements A1 and B1.
~B3 is shown in FIG. 2, and EL elements A2 and B4. B5
The details are shown in Figure 3. In both figures, the curve shown by a solid line is the luminance-voltage characteristic, the curve shown by a broken line is the luminous efficiency voltage characteristic, and the code of each curve corresponds to the code of the EL element.

From the results shown in FIGS. 2 and 3, the EL elements Al and A2 according to the present invention have a low threshold voltage (Vth) for starting light emission, a fast rise in brightness, and a significantly high final brightness. It is clear that it exhibits high luminous efficiency. On the other hand, the EL elements B1 and B4, which did not have a niobium oxide layer, had a high threshold voltage for starting light emission, a slow rise in brightness, and both the final brightness and light emitting efficiency.
It can be seen that this is significantly inferior to L elements AI and A2.

Further, EL element B2. in which the dielectric layer in contact with the niobium oxide layer is a single layer. B5 and E where both thin film layers of the dielectric layer have opposite stratigraphy.
In the L element B3, the threshold voltage for starting light emission is relatively low;
It can be seen that the luminance rises quickly and reaches high luminance, but the luminous efficiency is considerably inferior to EL elements AI and A2.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a structural example of an electroluminescent device according to the present invention, FIG.
The figure is a luminance 1 luminous efficiency-voltage characteristic diagram of the same elements of Example 2 and Comparative Examples 4.5. 2.7... Electrode, 3,5... Dielectric layer, 4... Light emitting layer, 5a... Insulating thin film layer, 5b... Semi-insulating thin film layer, 6... Niobium oxide layer Patent applicant: Hitachi Maxell, Ltd. (1 other person)

Claims (3)

[Claims] (1) In a double-insulated electroluminescent element in which a light-emitting layer and dielectric layers sandwiching the light-emitting layer from both sides are arranged between opposing electrodes, at least one of which is transparent,
A niobium oxide layer is formed between at least one electrode and the dielectric layer, and the dielectric layer located between the niobium oxide layer and the light emitting layer is in contact with the semi-insulating thin film layer that is in contact with the niobium oxide layer and the light emitting layer. An electroluminescent element characterized by having a two-layer structure with an insulating thin film layer. (2) Y_2O_3, Ta_2O_ in which the semi-insulating thin film layer is formed by electron beam evaporation or sputtering
3, Sm_2O_3, BaTiO_3, BaTa_2O
The electroluminescent device according to claim 1, comprising a thin film selected from _6. (3) SiO in which the insulating thin film layer is formed by electron beam evaporation, sputtering or CVD
2, Si_3N_4, Al_2O_3, AlN, SiA
The electroluminescent device according to claim 1 or 2, comprising a type of thin film selected from lON.