JPH01206596A - Film type electroluminescence element - Google Patents

Abstract

PURPOSE:To have an EL element with a low light emission start voltage, lesser leak current, large margin, excellent stability, and high durability by including titanium nitride in the insulation layer together with titanium oxide. CONSTITUTION:A base plate 1 consisting of non-alkali glass is used, whereon a clear electrode 2 consisting of In-Sn composite oxide film is formed previously, and on this electrode 2, an insulation layer 5 containing chiefly titanium oxide and further titanium nitride is formed in a specific area by ion beam sputtering method under certain conditions, and on this layer 5 a light emitting layer 4 consisting of ZnS:TbF3 is formed, and further thereupon a similar insulation layer 6 is formed by ion beam sputtering method in a similar. On this layer 6, in turn, a back face electrode 3 consisting of Al film is formed by resistance heating evaporation method, to prepare a film EL element of double insulation type as illustrated. In this element, the whole insulation layer is in electrically stable crystal structure, and it exerts excellent characteristics.

Description

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

[Conventional technology]

This type of thin film EL element has a structure in which a light emitting layer and an adjacent insulating layer are interposed between a pair of opposing electrodes, at least one of which is transparent and one of which is usually patterned. have.

In addition, the above-mentioned insulating layer may be provided only on one side of the light emitting layer (table insulation structure), or may be provided on both sides (double insulation structure). Such an EL element is driven by applying an alternating current electric field higher than the light emission starting voltage of the light emitting layer between a pair of electrodes to cause it to emit light, and by making the emitted light appear on the surface of the substrate on the transparent electrode side. The pattern is displayed.

By the way, it is desirable that the insulating layer of the above-mentioned EL element has a high dielectric strength voltage, and also that the voltage applied to the element is inversely proportional to the capacitance of the luminescent layer and the insulating layer. Therefore, in order to effectively apply voltage to the light emitter layer and to reduce the voltage applied to the entire device, it is necessary to use dielectric properties that have a high relative dielectric constant and low dielectric loss. It is hoped that it will be of excellent quality.

A typical insulating layer that can relatively meet these required characteristics is a titanium oxide (Tie) thin film formed by sputtering or the like (unsatisfactory literature).

[Problem to be solved by the invention]

However, in conventional EL devices using an insulating layer made of the titanium oxide thin film described above, the emission starting voltage is high, for example, about 200 V in a double insulation type, and the leakage current is large, leading to a margin, that is, dielectric breakdown from the start of emission. There have been problems in that the voltage range is narrow and stability is lacking, durability is poor especially as the display area becomes larger, and luminance is insufficient. ``This invention was made to solve the above problems,
In those equipped with an insulating layer mainly made of titanium oxide,
The object of the present invention is to provide an EL element that has a low emission starting voltage, a small leakage current, a large margin, excellent stability, high durability, and high brightness.

[Means to solve the problem]

In the process of intensive study to achieve the above object, the inventors first discovered that in an EL element equipped with an insulating layer made of a conventional titanium oxide thin film, oxygen vacancies are inevitably formed in the thin film. It was discovered that this defect is the main cause of increasing leakage current and impairing the stability of the device. Therefore, as a result of further investigation based on this knowledge, we found that if the insulating layer contains titanium oxide as its main component and other specific components, this specific component will supplement the above-mentioned defective parts and improve electrical performance. The inventors discovered that a stable crystal structure is formed, which significantly improves the stability and durability of the device, and also significantly reduces the emission starting voltage and significantly increases the luminance, leading to the creation of this invention. .

That is, the present invention provides a thin film EL element in which a luminescent layer and an adjacent insulating layer mainly made of titanium oxide are interposed between a pair of opposing electrodes, at least one of which is transparent, in which the insulating layer is This invention relates to a thin film type EL element characterized by containing titanium nitride as well as titanium oxide.

[Structure and operation of the invention]

The drawing shows a thin film type EL with double insulation structure to which this invention is applied.
An example of the element is shown.

In the figure, l is a transparent substrate made of a glass plate or the like, and 2 is rn2'off -5nO2 with a thickness of about 100 to 300 nm.
Transparent electrode made of thin film, such as ITO thin film, 3 is AN
The thickness of thin film or ITO thin film is 100 to 500n.
The back electrode has a thickness of approximately m and is patterned into a shape corresponding to the display pattern.

4 contains a small amount of luminescence activator such as rare earth fluoride or manganese in a matrix made of zinc sulfide (ZnS), for example, ZnS:TbF3 (green luminescence),
ZnS: SmFs (red emission), Zns: Mn (yellow-orange emission), ZnS: TmF3 (blue emission), Z
ns: PrF+ (white light emission), ZnS:Dy
Thickness of Fs (yellow luminescence) etc. is 300 to 1.00
This is a light emitting layer with a thickness of about 0 nm.

Reference numeral 5.6 denotes an insulating layer adjacent to the front and rear surfaces of the light emitting layer 4, which is composed mainly of titanium oxide (TiO□) and further contains titanium nitride (TiN), and has a normal thickness of about 200 to 500 nm. Formed of a thin film, the insulating layer 6 on the back side also extends to the side surface of the light emitting layer 4, and this and the insulating layer 5 on the front side completely isolate the light emitting layer 4 from the external atmosphere. It has become.

In the EL element with the above configuration, as described above, '4t! Since the A-edge layers 5 and 6 are made of thin films mainly composed of titanium oxide and further containing titanium nitride, the emission starting voltage is low at around 160V, and the margin is large and stable at 80V or more, as shown in the examples below. It exhibits excellent durability and extremely high luminance.

In other words, in an EL element with a conventional structure in which both insulating layers are simply titanium oxide thin films formed by sputtering or the like, it is inevitable that some oxygen vacancies will occur in the titanium oxide thin film. As a result, the leakage current increases, and as in the comparative example described later, the emission starting voltage increases to about 200V and the margin also increases to 6.
The voltage becomes narrow at around 0V, resulting in lack of stability and low luminance. On the other hand, in the EL device of the present invention, the portions of the titanium oxide that form the main part of the insulating layer, which would originally be oxygen-deficient portions, become titanium nitride through the introduction of nitrogen atoms, so that the entire insulating layer is It has an electrically stable crystal structure and exhibits the excellent performance described above.

Conventionally, a thin film type E is used to form such an insulating layer 5.6.
Although it is possible to adopt any of the various vacuum thin film formation methods used to form each layer of the L element, from the viewpoint of improving dielectric properties and insulation resistance, titanium oxide is used as the target and reactive gas An ion beam sputtering method using nitrogen gas together with oxygen gas is preferable.

Generally, the ion beam sputtering method ionizes a rare gas such as argon, accelerates and focuses the ion, and collides with a target in a vacuum chamber to sputter target material. A thin film is formed by depositing a target substance on the surface of the substrate. and,
When forming an oxide thin film, it is common to use the same oxide material for the target, and to use oxygen gas as a reactive gas together with the above-mentioned rare gas in order to prevent the formation of oxygen vacancies. However, in titanium oxide thin films, even if oxygen gas is used as the reactive gas as described above,
The generation of oxygen vacancies to some extent cannot be avoided, and these vacancies cause the above-mentioned problems.

On the other hand, when nitrogen gas is used together with oxygen gas as the reaction gas as described above, when only oxygen gas is used, nitrogen atoms from the nitrogen gas are introduced into the oxygen-deficient parts to form titanium nitride. Therefore, an electrically stable crystal structure free from defects is formed as a whole of the insulating layer, and an insulating layer that can sufficiently exhibit the above-mentioned effects can be obtained.

The usage ratio of the above nitrogen gas is 20 to 60% by volume (Nz / (Ar+0□+Nz) of the total atmospheric gas, that is, the total amount of rare gas such as argon, oxygen gas, and nitrogen gas.
If it is too small, oxygen-deficient structures will remain and the above-mentioned effect will not be fully exhibited.
On the other hand, if the amount is too large, the ratio of titanium nitride becomes too large, and the properties of the insulating layer are deteriorated.

Other conditions for such ion beam sputtering method include vacuum degree lXl0-' to 5x10-'To
It is preferable to set the deposition rate to about rr, the substrate temperature to about 20 to 300° C., and the film formation rate to about 1 to 10 nm/min.

Note that as the target material, titanium oxide is usually used as described above, but it is also possible to use metallic titanium in some cases.

The insulating layers 5 and 6 thus formed preferably have a titanium oxide:titanium nitride weight ratio of 1:0. OO5~0.05
It is preferable that the composition be within a certain range.

The other layers of the EL element, that is, the transparent electrode 2, the luminescent layer 4, and the back electrode 3, are formed using suitable vacuum thin film forming means,
For example, various vacuum evaporation methods such as electron beam evaporation and resistance heating evaporation, ion blating methods, various sputtering methods such as high frequency sputtering and ion beam sputtering, and various CVD methods such as plug 7 CVD and optical CVD.
(Chemical Vapor Deposit
on) method.

In addition to the illustrated double insulation type thin film EL device having insulating layers on both sides of the light emitting layer, the present invention also applies to a double insulation type thin film EL device having an insulating layer on both sides of the light emitting layer, a table insulating type in which the insulating layer is only on one side of the light emitting layer, a light emitting layer or a light emitting layer. and one electrode is laminated with an insulating layer between each layer.
The present invention is similarly applicable to elements configured in multiple layers or more.

〔Effect of the invention〕

As described above, in the thin film EL device of the present invention, the insulating layer is mainly composed of titanium oxide and further contains titanium nitride. In comparison, the light emission starting voltage is low, the leakage current is small, the margin is large, the material has excellent stability, high durability, and extremely high light emission brightness can be obtained.

〔Example〕

Examples of the present invention will be specifically described below in comparison with comparative examples.

Examples 1 to 3 A substrate made of alkali-free glass with a thickness of 200 nm on which a transparent electrode (specific resistance 10 Ω/cd) made of an ITO film with a thickness of 250 nm was previously formed on one side was used, and the transparent electrode of this substrate was An insulating layer with a thickness of 400 nm mainly composed of titanium oxide and further containing titanium nitride was formed on an area of 10 by the ion beam sputtering method under the conditions shown in Table 1 below.
A 500 nm thick phosphor layer made of ZnS:TbF3 (TbF3 content: 3% by weight) is formed on this insulating layer by electron beam evaporation, and the above phosphor layer is further formed on this phosphor layer. An insulating layer similar to the above is formed by a similar ion beam sputtering method,
Finally, a back electrode made of an AI film with a thickness of 200 nm was formed by resistance heating vapor deposition to produce a double-insulated thin film EL device having the configuration shown in the drawing.

Comparative Example Examples 1 to 3 are the same except that the insulating layers on both sides of the light emitter layer are titanium oxide thin films with a thickness of 400 nm formed by ion beam sputtering under the conditions shown in Table 1 below.
A double-insulated thin film EL device was fabricated in the same manner as in Example 3.

Table 1: 5K for each EL element of the above examples and comparative examples.
An alternating current pulse voltage of Hz was applied, and the emission starting voltage, margin (difference between the emission starting voltage and breakdown voltage), and maximum brightness were measured. The results are shown in Table 2 below along with the insulating layer composition of each EL element.

Table 2 From the results in Table 2 above, it is clear that the EL devices according to the present invention (Examples 1 to 3) have a lower luminescence starting voltage than the EL devices with the conventional structure (comparative example) in which the insulating layer is made only of titanium oxide. It is clear that the luminance is significantly low, the margin is wide, the stability and durability are excellent, and very high luminance can be obtained.

In the EL device of the present invention, the insulating layer has a two-layer structure, one of which is a thin film containing titanium oxide and titanium nitride as described above, and the other layer is a thin film containing titanium oxide and titanium nitride as described above.
, S 10z -Y203- Ta2O, , Si, N4
It is also possible to make changes such as using other thin films such as , and thereby the margin can be further widened.

[Brief explanation of the drawing]

The drawing is a sectional view showing an example of a thin film electroluminescent device according to the present invention. 2...Transparent electrode, 3...Back electrode, 4...Light emitter layer, 5.6...Insulating layer Patent applicant Hitachi Maxell, Ltd.

Claims (5)

[Claims] (1) In a thin film electroluminescent device in which a luminescent layer and an adjacent insulating layer mainly made of titanium oxide are interposed between a pair of opposing electrodes, at least one of which is transparent, the insulating layer is A thin film electroluminescent element characterized by containing titanium nitride as well as titanium oxide. (2) The thin film electroluminescent device according to claim 1, wherein the insulating layer is provided on both upper and lower sides of the light emitting layer. (3) The weight ratio of titanium oxide to titanium nitride in the insulating layer is 1.
: The thin film type electroluminescent device according to claim 1 or 2, which is in the range of 0.005 to 0.05. (4) Any one of claims (1) to (3), wherein the insulating layer is formed by an ion beam sputtering method using titanium oxide as a target and nitrogen gas together with oxygen gas as a reactive gas. A thin film electroluminescent device according to claim 1. (5) Nitrogen gas is 20% of the total atmospheric gas including rare gases.
5. The thin film electroluminescent device according to claim 4, wherein the thin film electroluminescent device occupies 60% by volume.