JPS6244986A - Manufacture of thin film el 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 (Industrial Field of Application) The present invention relates to an AC-driven thin film EL device used as a light emitting display device or a surface light source, and particularly relates to a low voltage drive device using a novel insulating layer thin film. , and a highly reliable method of manufacturing a thin film EL device.

(Prior art) Figure 2 shows the cross-sectional structure of a typical AC-driven thin film EL element (Nis.I.D.74 Digest of
Technical paper 184 pages, (STD 74 di
gest oftechnical papers))
. In the figure, the thin film EL element has a transparent electrode 22 made of an ITO film or a NESA film on a transparent glass substrate 21, a thin film first insulator layer 23, a light emitting layer 24 such as a ZnS:Mn or ZnS:TbF3 thin film, and further on top of that a transparent electrode 22 made of an ITO film or a NESA film. Thin film second insulator layer 25, Al
It has a multilayer thin film structure consisting of a back electrode 26 such as a thin film. Light emission can be obtained by applying an alternating current voltage between both electrodes of this element. This light emission occurs when electrons in the light emitting layer, which are raised to the conduction band by a high electric field of about 2 MV/cm and accelerated at high speed, collide and excite light emitting centers such as Mn. The emission color is determined by the energy level difference between the excited state and the ground state of the emission center. For example, Mn emits yellow-orange light, while Tb emits green light.

In addition, the insulator layer in Figure 2 prevents excessive current from flowing to the light-emitting layer and destroying the device, and also improves light-emitting efficiency by superimposing the electric field due to polarization on the externally driven AC electric field. This also brought about improvements in light emission characteristics, such as increased nonlinearity of voltage-luminance characteristics, and the adoption of this insulator layer made thin-film EL devices practical for the first time. Traditionally, Y2O5, Al2O3, 5iaN have been used as insulator layers.
4. Ta205. Sm20a, TiO2゜BaTi0a
, 5rTiOa, PbTiOa, etc. are formed and used by vacuum evaporation or sputtering.

(Problems to be Solved by the Invention) The insulator layer is very important for AC driven thin film EL elements. In terms of the operating characteristics of the EL element, the insulator layer can be understood as a capacitor in terms of an equivalent circuit.

That is, the external voltage applied between both electrodes is divided and applied to each layer in inverse proportion to the respective capacitance of the insulating layer and the light emitting layer. Therefore, in the case of an element configuration in which the capacitance of the insulator layer is small, an extremely high external voltage is required because the external voltage is not effectively applied to the light emitting layer. Furthermore, since the current that flows in the light emitting layer in an alternating current manner and contributes to light emission is proportional to the capacitance of the insulator layer, high brightness light emission cannot be obtained if the capacitance of the insulator layer is small. Therefore, increasing the capacitance of the insulator layer is important for lower voltage driving and higher brightness of the EL element. Tail Y2 is usually used to increase the capacitance of the insulator layer.
o3. The use of extremely thin films of Al2O3, Si3N4, etc. is inappropriate because it causes significant dielectric breakdown of the EL element, and it is preferable to construct the insulating layer with a material having a high dielectric constant. For example, about 2
It has been reported that a low-voltage driven EL device can be realized by employing a P)) Tioa thin film with a dielectric constant of 0.00 as an insulating layer (IEE Transactions on・Electron Devices,
(IEEE Tran,s, ElectronDev
ices ED-28, p69g (1981)),
(Japanese Patent Application Laid-Open No. 56-45595). However, in order to form a PbTi0a thin film with a high dielectric constant for EL devices by sputtering, as reported in the above-mentioned literature, there is a compositional deviation due to sputtering film formation, which impedes reproducibility.
In order to obtain a crystalline phase with a high dielectric constant, a very high substrate temperature of about 600°C is required. These two problems are extremely severe for film formation on large-area substrates required for display panels, and it is difficult to achieve sufficient productivity. Furthermore, the sputtering of PbTiOa causes problems such as corrosion of the substrate glass and blackening of the ITO transparent electrode, making it difficult to use as an insulator layer for thin-film EL devices.

In addition, due to its high dielectric constant, a relatively thick thin film of PbTi
Even if a 0A thin layer is adopted, it is difficult to completely eliminate minute defects such as pinholes in films created by sputtering or other film formation methods, and these defects tend to be the core of the device's destruction due to energization. there were. Therefore, although it is attractive to employ a high dielectric constant thin film such as PbTiOa as an insulating layer in view of the characteristics of an EL element, it has been difficult to employ it industrially.

The present invention realizes a thin-film EL device using a high dielectric constant thin film as an insulating layer, which solves the various problems described above, and provides a low-voltage drive, high-luminance, low-cost, and highly reliable EL display device. The purpose is to provide a manufacturing method.

(Means for Solving the Problem) The method for manufacturing a thin film EL device of the present invention includes a light emitting layer such as a ZnS:Mn thin film and one side of the light emitting layer between two electrodes, at least one of which is translucent. Alternatively, in a method for manufacturing a thin film EL element in which thin film insulator layers are formed on both sides,
A step of repeating multiple times a process of applying a precursor solution in which an organic metal containing at least Ti is dissolved in a solvent and heating and baking to form an oxide containing Ti in order to form at least one of the insulating layers. A method for manufacturing a thin film EL device, the method comprising:

(Function) The precursor solution for forming the insulator layer of the EL element of the present invention is an oxide containing Ti having a high dielectric constant, such as TiO2.
, PbTiOa, BaTiO3, 5rTiOa, solid solutions thereof, PZT, PLZT, etc. are formed by heating and firing, and organic titanium compounds such as titanium alkoxides, or these compounds are mixed in p-diketones as a solvent. , Pb, Ba soluble in diketones
, Sr.

5 to 20 in terms of oxides that produce compounds such as Zr and organometallic compounds containing Ti and Pb, Ba, Sr, Zr, etc.
It contains about % by weight. This precursor solution is IT
By applying a thin layer to a substrate such as glass on which a lower electrode such as an O film is formed by a dipping method, a spin code method, a roller coat method, etc., and then heating and baking at 450°C to 700°C. A thin oxide film containing Ti is obtained. This process is repeated at least twice to obtain a predetermined film thickness. Thereafter, a light-emitting layer and the like are formed in the same steps as those for producing a normal thin-film EL device, thereby obtaining the thin-film EL device of the present invention.

By adopting an organometallic thermal decomposition method using precursor solution coating to form the insulator layer, it is possible to adjust the stoichiometric ratio and composition ratio necessary to achieve a high dielectric constant using film forming methods such as sputtering. It is comparatively easy to carry out, and it is possible to obtain a thin film having a dielectric constant of about 10 to 30. The film created using this method has very few defects such as pinholes.
In addition, by repeating coating and firing, even if a minute defect occurs in a single process, it can be repaired, thereby completely eliminating defects such as pinholes, which pose a practical problem. In addition, conventional thin-film EL devices are susceptible to element destruction due to defects such as scratches and grains on the substrate glass surface, numerous pinholes occurring in the ITO film, and unevenness such as etching steps on the ITO electrode. It tended to be easy.

The precursor solution used to form the first insulator layer thickly adheres to holes such as scratches, pinholes, and steps on the substrate, which has the effect of repairing irregularities and forming a smooth surface. It is effective in preventing dielectric breakdown.

As described above, the manufacturing method of the present invention allows a defect-free, high-permittivity insulating layer to be formed over a large area at a relatively low cost, resulting in an excellent thin-film EL element that can be driven at low voltage, has high brightness, and is highly reliable. can be realized.

(Example) Fig. 1 shows a cross section of a thin film EL device prepared in an example.
The process will be explained below. A transparent electrode 12 is formed by forming a film of about 0.2 microns of ITO on a Corning 7059 glass substrate 11.
was formed. Tetrabutoxytitanium: Ti (OC4H9
)4 and lead acetate:Pb(CH3COO)2 as Ti/Pb
Weigh it so that the ratio is 1 and put it in xylene.
Powdered reaction product heated to 0-140°C:
Pb-Ti02(OC4Hc+)2 was obtained. Dissolve this in acetylacetone and PbTi0a equivalent concentration 1 equivalent amount %
A PbTi0a formation precursor solution was prepared. This solution was applied to the substrate using a roller coater. Then 5
It was fired by heating in a tunnel furnace maintained at 50°C.

The holding time at the heating temperature of 550°C is about 30 minutes. This coating and firing process was repeated five times to obtain a PbTiO3 film 13 with a thickness of 0.6 microns. The dielectric constant of this film is approximately 20
0, and a large dielectric constant was achieved for a thin film.

Next, a ZnS:Mn thin film 14 containing 1 mol % of Mn was formed to a thickness of 0.3 microns by vacuum evaporation. Thereafter, a Ta-8i-0 film was formed as the second insulating layer 15 to a thickness of 0.2 microns by sputtering using a target prepared by mixing and sintering Ta205 and 5i02 powders.

Finally, an upper electrode 16 of AI was formed by vapor deposition to obtain the EL element of this example.

A 500 Hz alternating current pulse was applied to this device to investigate its light emission characteristics. The emission starting voltage was 60V, and when 90V was applied, a brightness of 700 cd/m2 was obtained. Furthermore, in the case of a single-line edge type element in which the second insulating layer was not formed, the luminous efficiency and luminance reduction due to long-term use were slightly inferior, but the luminescence starting voltage could be lowered to about 45V.

In this example, a Ti-containing oxide thin film produced by organometallic thermal decomposition was used as the first insulator layer formed prior to the formation of the light emitting layer. The thin film may be formed as a second insulating layer after the formation of the light emitting layer, but in this case, the luminance of the light emitted decreased, probably due to reaction with the light emitting layer during heating and baking of the precursor solution. It is expected that this problem will be improved by examining the raw materials of the precursor solution, the heating process, etc., but at present it is preferable to use it only as an insulator layer formed before forming the light emitting layer.

In addition, although we have described the case where a PbTi0a film is formed using an organometallic solution, the TiO2
, 5rTiOa, BaTiO2, PZT, PLZT, etc., or composite films thereof can be formed, and the same effects as in this example can be obtained.

(Effects of the Invention) According to the present invention, a thin film EL element with low driving voltage can be realized. In addition, the device obtained according to the present invention was less prone to dielectric breakdown and had good reliability. The manufacturing method using solution coating is also suitable for film formation on a large-area substrate, and has a large cost advantage compared to the usual sputtering method, so the present invention has great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a thin film EL for explaining an embodiment according to the present invention.
This is a cross-sectional structure of the element. FIG. 2 shows a cross-sectional structure of a conventional thin film EL device. 11.21...Glass substrate, 12.22...Transparent electrode, 13...Organometallic pyrolysis PbTi0a film, 2
3... First insulator layer, 14.24... Light emitting layer, 15.25... Second insulator layer, 16.26...
Back electrode Figure 1

Claims (1)

[Claims] Manufacture of a thin film EL device in which a light emitting layer such as a ZnS:Mn thin film is formed between two electrodes, at least one of which is translucent, and a thin insulator layer is formed on one or both sides of the light emitting layer. In the method, in order to form at least one of the insulating layers, a precursor solution in which an organic metal containing at least Ti is dissolved in a solvent is applied, and heated and baked to form a Ti
1. A method of manufacturing a thin film EL device, comprising the step of repeating a process of forming an oxide containing oxide a plurality of times.