JPS61269896A - Thin film luminescence element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a thin film light emitting device, and in particular, a thin film light emitting device that achieves high brightness, low voltage, and high reliability by improving the structure of an insulating layer. It is.

Hereinafter, a thin film light emitting device may be referred to as a thin film EL device.

[Background of the invention]

FIG. 2 shows the basic cross-sectional structure of a conventional thin film EL element. The structure of the thin film EL element will be specifically explained based on FIG.
A first insulating layer 3 made of Nae Sigh or the like is formed by sputtering or electron beam evaporation. A light emitting layer 4 is formed on the first insulating layer 3 .

In the case of yellow-orange light emission, this luminescent layer is formed by beam beam or sputtering of sintered pellets doped with Mn as an additive in zus. In addition, as a sintered pellet for forming a light emitting layer,
TbFs, 'rbP (emission color:
green), SmFs (emission color: red), TmF'3 (emission color:
There are also those doped with blue). On the light emitting layer 4, a first
A second insulating layer 5 made of the same material as the insulating layer 3 is laminated, and a back electrode 6 made of λt, Au, etc. is further deposited thereon. An AC power source is connected between the transparent electrode 2 and the back electrode 6, and the thin film gL element is driven. 2 like this
．． [Thin-film EL elements with an insulating structure are already on the market in some areas, but they still have low luminance, high driving voltage,
There are problems such as low luminous efficiency and low device reliability. For this reason, active research and development is currently being carried out with the aim of improving light emitting characteristics such as higher brightness, lower voltage, higher efficiency, and higher reliability.

This type of thin film EL element is disclosed in Japanese Patent Application Laid-Open No. 58-216, for example.
It is described in Japanese Patent Application Laid-open No. 391, Japanese Unexamined Patent Publication No. 52-129296, and the like.

The method of achieving such goals in thin film BL element characteristics lies in how to fabricate a high-quality insulating layer or how to select an optimal insulating film configuration. because,
The light emission of the thin film gL element is approximately 10'\/Crr1 in the light emitting layer.
This is because an insulating layer having a higher dielectric breakdown strength is required for this purpose.

By the way, as the above-mentioned 48 edge layer material, conventional SIO is used.

SiO2*YzOst At403s 5isN4 and the like are used, but since these insulating layer materials have a small dielectric constant, the partial voltage of the voltage applied to the insulating layer becomes extremely large. Therefore, there is a drawback that an extremely high driving voltage is required to cause the light emitting layer to emit light.

Therefore, as a method of lowering the driving voltage, Tax 0!1. P')T 10s
.

A thin film EL device using 8rTiOsp PbTiOs and 20 g of BaTa has been studied, but aging treatment before light emission (additives such as Mu, TbF in ZuS) has been studied.
In the process for uniformly diffusing 3°8mF3, TmFs, etc., dielectric breakdown is likely to occur, resulting in pixel destruction.

In addition, the dielectric properties of these insulating layers generally vary greatly depending on the formation conditions, and in many cases the composition shifts, resulting in a decrease in packing density and defects such as pinholes and microcracks, resulting in poor dielectric breakdown voltage and moisture resistance. It has been found that there is a problem in which deterioration of the thin film EL element occurs, which has a large effect on the life characteristics of the thin film EL element.

[Purpose of the invention]

An object of the present invention is to provide a novel thin film FJL element that eliminates the drawbacks of the insulating layer of conventional thin film BL elements and has dramatically improved element characteristics and reliability.

[Summary of the invention]

As a result of studies to solve the problems of the insulating layer of conventional thin-film EL devices, the present invention found that in order to obtain a thin-film EL device with high brightness, low voltage, and high reliability, at least one of the insulating layers is It has been found that this can be achieved by creating a layered structure, or by combining materials with large and small dielectric constants as materials for the insulating layer, or by combining materials with high and low dielectric breakdown strengths.

First, the present inventors used ZnS, which emits yellow-orange light, in the light-emitting layer.
:Mn0.5μm is used, and the insulating layer has a small dielectric constant Vs.
S i02 (g, = 40) 0.5μm t
- A thin film KL element was prepared using the above method. As a result, no light emission was observed even when the drive voltage was set to tl-301 or higher. However, when 5fOz was used for the insulating layer, no dielectric breakdown of the pixel occurred at all. This means that a material with a small dielectric constant has a large dielectric breakdown voltage. Therefore, 3r'l'10s (6r=
As a result of fabricating a thin film BL element using 140), it was observed that the driving voltage decreased to approximately 100"/2, but it was found that the pixels were significantly destroyed during the aging process. This indicates that
It has been found that materials with a high dielectric constant are expected to reduce driving voltage, but their dielectric breakdown voltage is low, resulting in a decrease in device reliability.

Therefore, the present inventors speculated that it would be possible to take advantage of the characteristics of each material by combining a material with a high dielectric constant and a material with a low dielectric constant, that is, a material with a dielectric breakdown voltage, and creating a laminated structure for the insulating layer.

The results are shown in Figures 3-5. Figure 3 shows the voltage of the insulating layer -''#Il current when S r'111Q3 (e, = 140) with a large dielectric constant and 8i0z (ε, ±401) with a small dielectric constant are laminated to form a 2141 film. Characteristics (v-1%
gender). From this V-1 characteristic, the leakage current and dielectric breakdown voltage (the voltage at which the leakage current suddenly rises) of the insulating film can be read. The leakage current in the insulating layer should be as small as possible. This is because when a thin film BL element is used, current flows through the light emitting layer, promoting deterioration of the light emitting layer.

As is clear from this figure, S rT its (0−
5μm), the leakage current is large and the dielectric breakdown voltage is small. Therefore, a layer of 81020.10 μm was laminated.

Two-layer structure of the present invention 5rTiOs (0.4 μm), S
i (h(0,10pm) insulating film (hereinafter, 3rTiO
It can be seen that by using Sing, the leakage current of the s/5fox film is much smaller and improved compared to that of the Ta*Os film. Figure 4 is 8r
The apparent dielectric constant of the TiOs/8i012 layer film was determined. As is clear from this, by changing the film thickness ratio of 8rTiOs and 5fOz, Sr′I”i
The apparent relative permittivity of the 0s/3i0a film is 5ioz and 5r.
It has been found that the dielectric constant of Tios can be controlled arbitrarily, and an element with an arbitrary driving voltage can be created.

FIG. 5 shows the relationship between the drive voltage and the thickness of the insulating layer when insulating layers with different fs electric conductivity are used. In order to eliminate pinholes in the insulating layer, we have confirmed that the thickness of the insulating layer needs to be 0.5 μm or more, which will be described later, and the relative dielectric constant to reduce the driving voltage to 150 V or less. is 30
I realized that I needed to do more than that.

From the above results, the dielectric constant of the two-layer film must be 30 or more, and in order to obtain this dielectric constant, the dielectric constant of one of the materials in the two-layer film needs to be at least 't-40. I understand.

Furthermore, when materials with different dielectric constants are laminated to form a two-layer insulating film, basically no matter which insulating film is used as the lower layer,
It was confirmed that the l-14I property and dielectric constant did not change. However, when producing a thin film EL element, the present inventors sometimes observed a phenomenon of peeling between an electrode (transparent electrode, back electrode) and an insulating layer during the production process. As a result of examining the cause, it was revealed that materials with a high specific git ratio have a low adhesion with the electrode. The results are shown in FIG. As is clear from this, when the dielectric constant is 15 or more, the dielectric constant becomes about 1/2 that of a material with a small dielectric constant. From this result, in the present invention, when using a 211 insulating film, a film with a small dielectric constant of 15 or less is used on the electrode side. Therefore, the light-emitting layer is very attractive! Create a structure in which it is sandwiched between two parts with a large ratio. It has been revealed that by adopting such a structure, there is no peeling and the characteristics of each insulating layer can be fully brought out.

In addition, in the present invention, pinholes occur in the conventional single insulating film, moisture in the air enters when the device is used (light emitting operation), and the reliability of the device is deteriorated. This problem was solved by using a layered insulating film.

The results are shown in the table below.

Table This table shows the results of examining the pinhole density t, and it can be seen that by laminating different types of insulating layers, the pinhole density is reduced by an order of magnitude compared to a single layer film.

Above, we have described the characteristics of using a two-layer insulating layer that combines materials with large and small dielectric constants (large and small dielectric breakdown voltages) as an EL insulating layer. A thin film 3L element with high pressure and damage reliability is provided.

[Embodiments of the invention]

FIG. 1 is a cross-sectional configuration diagram of a display panel using thin film EL elements showing one embodiment of the present invention. Hereinafter, the process will be explained in accordance with the order of steps shown in FIG.

A transparent electrode 2 made of 8N02, InzOs, etc. is formed on a Corning+7059i substrate 1 to a thickness of about 2000 A and a sheet resistance of 10 to 2 Ω/hole. The most suitable forming method is the sputter link method or the electron beam evaporation method. When forming by sputtering method, the conditions are Ar+10wt as reaction gas.
*Reactive sputtering may be performed using Q2 and a target of Sn6 or In.

Next, in order to form a predetermined electrode pattern required for the EL element, the transparent electrode 2 is etched into strips arranged in parallel using a photo-etching technique. As an etching solution for the transparent electrode at this time, an HCl-HNOs-based etching solution or the like may be used.

First, on the transparent electrode 2, an adhesion insulating layer 7 having a small dielectric constant of SiOz'kO-1 μm is formed.

Next, S rT r Os (' r =
140) Q, 4 μmt- is formed, and the first insulating layer 3 is completed. Subsequently, a Zn8:Mn sintered body is deposited with an electron beam to form a light emitting layer 4, and then the substrate temperature is raised to 5500 ℃ and vacuum heat treatment is performed. Due to this heat treatment, ZuS
Mn, which is an additive, is uniformly diffused inside.

A second insulating layer 5 is formed on the light emitting layer 4. Similar to the first insulating layer, this second insulating layer is formed by first forming a main insulating layer 8 having a high dielectric constant, and subsequently forming the main insulating layer 8 having a high dielectric constant of 1! j The small adhesion insulating layer 7 is formed. Finally, the back electrode 6 is formed on the adhesive insulating layer 7. This back electrode 6 may be an At or Sn0w-based transparent conductive film.

IKH
After a sufficient aging process was performed by applying a Z positive arc wave voltage, the life characteristics of the EL element were measured. The results are shown in FIG. This figure 7 shows the series l1IlIJh with the luminance brightness after aging (initial brightness) being 100.
The figure shows the brightness when the insulating layer is made using the conventional technology. These are the characteristics of an Os single-layer film EL device.

It can be seen that the two-layer insulating layer structure EL element (&2) of the present invention prevents pinholes and cracks in the insulating layer and has a longer lifespan.

Furthermore, FIG. 8 shows the relationship between the pixel breakdown rate of a thin film EL display and the applied voltage during aging.

1 in the figure is a case where the conventional insulating layer shown in FIG. 1 is a single layer film, and it is clear that the EL display of the present invention does not suffer from pixel destruction during aging.

Furthermore, as a two-layer insulating film, PbTi0s (ε, = 120
)/8i0z (ε, = 4), and as a result of exploding the gL element and examining its characteristics, it was confirmed that high reliability was obtained, and it was revealed that it had the same effect as mentioned above. .

〔Effect of the invention〕

As described above, according to the present invention, the drawbacks of the insulating layer can be eliminated and the reliability of the device can be improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view of a conventional thin film EL element, FIG. 3 is a current-voltage characteristic diagram of the two-layer insulating film of the present invention, and FIG. 4 is a sectional view of an embodiment of the present invention. 2Bibrow marginal membrane (5rTiO
J# characteristic diagram 1 shows the relative dielectric constant of s /S iOi ), and Figure 5 shows a characteristic diagram showing the relationship between the driving voltage and the thickness of the insulating layer.
FIG. 6 is a characteristic diagram showing the adhesion of the insulating film to the electrode, FIG. 7 is a characteristic diagram showing the life span of the EL element of the present invention, and FIG. 8 is a characteristic diagram showing the pixel breakdown rate of the EL element of the present invention. 1... Glass substrate, 2... Transparent electrode, 3... First
Insulating layer, 4... Light emitting layer, 5... Second insulating layer, 6...
・Back electrode, 7th 3rd voltage<V) 4th Oσ, 2 σ・4 ρ, Otsu σ, 8
tθKaya 5th is Megami Shosaemi (7th territory) Kaya 6 Figure Hiyo @ Lee Kayo 8 Mouth lθ lθ2 /θ3 electric fi<v
)

Claims (5)

[Claims] 1. In a thin film light emitting device having a transparent electrode, a first insulating layer, a light emitting layer, a second insulating layer, and a back electrode stacked one after another on an insulating substrate, at least one of the first insulating layer and the second insulating layer is a two-layer structure. structure, and the electrode side has a relative permittivity of 1.
5 or less, and the light emitting layer side has a relative dielectric constant of 4.
A thin film light emitting device characterized in that it is made of 0 or more materials. 2. The thin film light emitting device according to claim 1, wherein both the first insulating layer and the second insulating layer have a two-layer structure. 3. In claim 1, the relative dielectric constant 1
5 or less materials are SiO_2, Y_2O_3, HfO_2
, Si_3N_4, and Al_2O_3. 4. In claim 1, the dielectric constant 4
0 or more materials are TiO_2, PbNb_2O_6, Sr
A thin film light emitting device comprising one or more of TiO_3. 5. The thin film light emitting device according to claim 1, wherein the total dielectric constant of the insulating layers having the two-layer structure is 30 or more.