JPH01286290A - Ac driven electroluminescent device - Google Patents

Abstract

PURPOSE:To enable the drive at low voltage and improve the stability by using a heat-resisting LB film having a specified characteristic for at least either of the 1st or the 4th insulating film of the 1st to 4th insulating films. CONSTITUTION:On a transparent base plate, a transparent electrode, a first insulating film having a high resistivity, a second insulating film having a low resistivity, a third insulating film having a low resistivity, a force insulating film having a high resistivity, and a back plate are successively laminated to form an EL display. A heat-resisting LB film having a thickness less than 5000Angstrom , and a dielectric strength not less than 1X10<6>V/cm, and a heat resistance not less than 300 deg.C is used for at least either of the 1st or 4th insulating film. As the LB film, a complete aromatic polyimide LB film is preferred. As the 2nd and 3rd insulating films, Ta2O5 is preferred. As the LB film is annealed at 300 deg.C or more after evaporating the luminous layer thereon, the heat resistance of the LB film is desirably not less than 300 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION -1 The present invention relates to an electroluminescent device (hereinafter referred to as an EL device).

More specifically, on a transparent substrate, a transparent electrode, a first insulating film with high specific resistance, a second insulating film with low specific resistance, a light emitting film,
In an EL display formed by sequentially laminating a low resistivity third insulating film, a high resistivity fourth insulating film, and a back electrode, at least one of the first or fourth insulating film has a thickness of 500 Å or less. Preferably 300 people, more preferably 200 people
Å or less, a dielectric breakdown strength of I x 106 V/cm or more, and a heat resistance of 300°C or more, preferably 400°C or more, more preferably 500°C or more!
i! The present invention relates to an AC-driven electroluminescent device characterized by using an AC-driven electroluminescent device.

Research into EL devices is being actively conducted in response to social demands such as making electronic equipment lighter, thinner, and smaller and improving display quality.

Recently, an insulating layer (
Thin film EL devices with a so-called double insulation structure, sandwiched between dielectric layers) with high brightness and long life, have been developed and put into practical use.

However, thin film EL devices with double insulation structure
Since a high AC voltage of around 0V is required, a dedicated high voltage IC must be used, which increases costs and
There is a problem that wide practical application is hindered.

In order to solve these problems and simplify the drive circuit,
There is a desire to develop thin film EL devices that can be driven at low voltages, and it has been reported that the operating voltage can be lowered to around 60V by using a ferroelectric material such as lead titanate; There are practical problems, such as the need to heat the substrate to a high temperature in order to obtain the desired rate.

The present invention has been made in view of the above-mentioned circumstances in order to obtain a stable and high-brightness AC-driven EL device that can be driven at a low voltage, and is a device that can be driven on a transparent substrate. , a transparent electric bridge, a first insulating film with high specific resistance, a second insulating film with low specific resistance, a light emitting film, a third insulating film with low specific resistance, and a fourth insulating film with high specific resistance. In an EL display formed by sequentially laminating a film and a back electrode, at least one of the first or fourth insulating film has a thickness of 1000 Å or less and a dielectric breakdown strength of l.
The present invention relates to an AC-driven electroluminescent device characterized by using a heat-resistant polymer LB film having a heat resistance of X106 V/an or more and a heat resistance of 300° C. or more, preferably 400° C. or more, more preferably 500° C. or more.

Examples The light-emitting film used in the present invention refers to the ffA group of the periodic table or the U
Created by the combination of at least one element selected from the elements belonging to Group B and the elements belonging to Group VII3.■
-It is a polycrystalline thin film made of a group compound. Said,
Since II-Vl group compounds can exist as solid solutions, solid solutions in which elements of the above compounds are replaced with other elements can also be used in the present invention. For example, Z in which part of Zn is replaced with Cd
nxCdl-xS (Q<x<1) and ZnSxSe1-x (0'<x<1) in which part of S is replaced with Se.
), and further ZnzCd t-zSySel-y
(0<y<l, O<z<1), etc.

Further, since non-stoichiometric compositional deviations may exist in these II-Vl group compounds, compounds in which the ratio of group (Ⅰ) to group (①) elements is not necessarily 1:1 may also be used in the present invention.

Usually, if-Vl group compound polycrystalline thin films are made of Mn, Cu
, Ag, etc., Tb, Sm, Er, Ho, Pr.

It is doped with an activator consisting of a rare earth metal such as Tm, a rare earth compound such as TbFa, SmF3゜ErFa, HOF3, PrFa, TmFa, etc., and if necessary, a halogen ion or a trivalent metal such as A1. It may also contain a co-activator such as salt.

By doping the If-Vl group compound polycrystalline thin film with an activator in this manner, it is possible to emit various types of light such as red, green, blue, yellow, and yellow-orange. At this time, it is preferable to select a II-Vl group compound with a large band gap, preferably 2.5 eV or more, so that the matrix ■-■ group compound does not absorb light in the visible light region. be. Examples of such II-Vl group compounds include ZnS.

In addition to Zn5e, other materials include ZnO, CaS, and SrS, but ZnS and Z
n5e is preferred.

The amount of doping activator is 10% of the ■-■ group compound polycrystalline thin film.
The co-activator is preferably 0.01 to 7 parts, preferably 0.2 to 3 parts, and the coactivator is preferably 0.0 parts by weight.
It is preferably 0.05 to 1 part, more preferably 1 to 3 parts. If the amount of the activator is less than 0.01 parts, the concentration of active sites contributing to luminescence will be low and effective luminescence will not be obtained, and if it exceeds 7 parts, the concentration of active sites will be too high and a saturation phenomenon will occur. n-v
Both are unfavorable since they tend to reduce the crystallinity of the r-group compound polycrystalline thin film. Furthermore, if the amount of the co-activator exceeds the above range, it is not desirable for reasons similar to those of the activator.

There are no particular restrictions on the method of doping with such an activator or co-activator, and iIN's method may be employed.

There are no particular limitations on the method of forming a thin film of II-Vl group compounds in the present invention, such as vapor deposition, sputtering, spray pyrolysis, coating, CVD (chemical vapor deposition), MOCVD (organic It is formed on a substrate by a thin film forming method using a metal vapor phase epitaxy method), an MBE method (molecular beam epitaxy method), an ALE method (atomic layer epitaxy method), or the like.

The crystal system of the ■-■ group compound used in the present invention is hexagonal system,
It exists in the form of a cubic system or a mixture thereof, but either case can be used.

Furthermore, it is known that the physical properties of the polycrystalline thin film, such as crystallinity, can be improved by heat treatment in various atmospheres, so the polycrystalline thin film may be used after being heat treated after forming the thin film.

The polycrystalline thin film used in the present invention is a crystalline thin film made by aggregating many small crystals with various orientations, but the small crystals must have a regular distribution of orientations and a fibrous or columnar structure. is desirable.

There is no particular limitation on the thickness of the polycrystalline thin film, but it is usually 1
00 to about 10 μm, and even 0.1 to l.

Approximately 0 μm is suitable.

Next, the substrate and electrodes will be explained.

There are no particular limitations on the substrate, and in addition to substrates made of general substrate materials such as glass, alumina, and quartz, metal plates, metal foils, plastic substrates, plastic films, group ■ semiconductors, ■-V group compound semiconductors, Polycrystalline wafers are used.

As electrodes, aluminum, gold, silver, platinum, palladium, indium, ln-Hg5 In-Ga, etc., as well as transparent electrodes such as tin oxide and tin/indium oxide (ITO), etc. can be used. Therefore, at least one electrode needs to be a translucent or transparent electrode.

Practically, it is preferable to use a substrate with a transparent electrode such as Nesa glass or ITO glass, and use a metal electrode made of AI, Ti, Ni-Cr, etc. as the back electrode. Of course, the electrodes on both sides may be transparent electrodes. In addition, when using the device as a display device, these two electrodes (transparent electrode and back electrode) are commonly used.
may be used in a pattern.

Next, we will discuss the insulating film. Said 2. The third insulating film has a specific resistance of 106 ρ and 109 preferably 105<p<1
07Ω'Cl1) and the membrane pressure is 500 to 10,000 people, preferably 3,000 to 10ooO people. The first and fourth insulating films are configured to have a specific resistance of 10''<ρ<101sΩ·0.
5iOz is preferable, and it is preferably produced by sputtering.

Said 2nd. As the third insulating film, Ta2e! + is preferred and is preferably produced by electron beam evaporation.

Next, the heat-resistant layer LB film, which is another high-resistance insulating film used in the present invention, will be explained.

In order to be used in practical AC-driven electroluminescent devices, the LB film must have a heat resistance of 300°C or higher, preferably 400'C or higher, more preferably 500°C or higher, and a dielectric breakdown strength of 1 x 106 V/e1m or higher. It is desirable that there be. When a light emitting layer is formed on LBHIfl, it is desired that the layer has heat resistance of 300° C. or more.

This is because when the light-emitting layer is deposited, it is done at a temperature of about 200°C, but after formation it is deposited at a temperature of 300°C or more, preferably 400°C.
This is because a method is used to improve the crystallinity by annealing at temperatures higher than 'C, more preferably 500°C or higher. The thickness is preferably 500 Å or less since there is a demand for driving at a voltage as low as possible and there is no cost advantage in using a thick LB film. 300Å or less and even 200Å
People are preferred. Heat resistance above 3°0°C and 1x
An LB film having a dielectric breakdown strength of 106 V/am or more can be selected from among the polymer thin films proposed by us in Japanese Patent Application No. 6390 (1986). It is preferable to use a thin film of a heat-resistant polymer having a precursor structure of a heat-resistant polymer containing a heterocycle, which is accumulated by the LB method to form a ring structure. A wholly aromatic polyimide thin film is particularly desirable.

Next, a method for manufacturing the LB film will be explained.

LB membranes are produced by spreading a film-forming substance on the water surface, compressing the substance spread on the water surface with a certain surface pressure to form a monomolecular film, and then transferring the film onto a substrate (Langmuir et al.
It can be produced using the Projet method). In addition, horizontal attachment method,
It can also be produced by methods such as the rotating cylinder method (New Experimental Chemistry Course Vol. 18, Interfaces and Colloids, pages 49B-508). Such a commonly used method can be used without particular limitation.

Normal EL devices have thick insulating films made of inorganic material on both sides of the light emitting layer, but in the EL device of the present invention, at least one of these insulating films has a thickness of 500 Å or less and a dielectric breakdown strength of 1 x 106 V. It is replaced by a heat-resistant polymer LB film having a temperature of /b or higher and a heat resistance of 300° C. or higher and a low resistivity insulating film. In the conventional LB film, L
BII! i! Although it has not been possible to form an inorganic layer without damaging the substrate, the heat-resistant LB film that we proposed earlier makes this possible. Of course, on top of the inorganic layer,
It is also possible to form a heat-resistant LB film.

Next, the EL device of the present invention will be explained in more detail based on examples.

Example 1 On a patterned ITO glass, 21 layers of B film, which is a 1:1 mixture of stearyl alcohol and a polyimide precursor synthesized from acid chloride of pyromellitic acid distearyl ester and diaminodiphenyl ether, were accumulated. was cured at 400°C for 1 hour to imidize. On top of this, tantalum oxide as a low-resistance insulating film was applied by EB evaporation.
000 people produced the film, and an additional 6000 people produced the light emitting layer ZnS:M.
Insulating layers of 5 iOz and 1,000 oz were formed by EB evaporation and sputtering, respectively. Finally, aluminum electrodes were attached to form an EL device. When we evaluated the brightness-voltage characteristics by applying an IKHz sine wave, the brightness rose from 90V, reached almost saturation at 120V, and the brightness was 200V.
Brightness sufficient for practical use was obtained at 0 Cd/cal.

Example 2 On patterned ITO glass, 21 layers of B film, which is a 1:1 mixture of stearyl alcohol and a polyimide precursor synthesized from acid chloride of pyromellitic acid distearyl ester and diaminodiphenyl ether, were accumulated. was cured at 400°C for 1 hour to imidize. On top of this, tantalum oxide as a low resistance insulating film, 6000 light emitting layers ZnS:Mn and tantalum oxide are all EB
The film was formed using a vapor deposition method. Furthermore, a 21M polyimide film was formed on this to serve as the other insulating film. Finally, aluminum electrodes were attached to form an EL device. When a sine wave of lKH2 was applied to evaluate the brightness-voltage characteristics, the brightness increased from 70V, reached almost saturation at 100V, and the brightness was 2000 Cd/c4, which was sufficient for practical use.

Effects of the invention At least one of the insulating films has a thickness of 500 Å or less, a dielectric breakdown strength of 1 x 106 V/e1) or more, and a heat resistance of 3
By providing a heat-resistant polymer LB film having a temperature of 00 DEG C. or higher and a low-resistance insulating film, it is possible to drive at a low voltage, and a stable, high-brightness group compound polycrystalline thin film AC-driven EL device can be obtained.

Claims (2)

[Claims] (1) A transparent electrode, a first insulating film with high specific resistance, a second insulating film with low specific resistance, a light emitting film, a third insulating film with low specific resistance, and a high specific resistance In an EL display formed by sequentially laminating a fourth insulating film of a resistor and a back electrode, the first
Alternatively, at least one of the fourth insulating films has a thickness of 500 mm.
An AC-driven electroluminescent device characterized by using a heat-resistant polymer LB film having a dielectric breakdown strength of 1×10^6 V/cm or more and a heat resistance of 300° C. or more. (2) The AC-driven electroluminescent device according to claim 1, wherein the heat-resistant polymer LB film is a wholly aromatic polyimide-based LB film.