JPH0562779A - Electroluminescence element - Google Patents

Abstract

PURPOSE:To improve the intensity irregularity of luminescence and suppress the occurrence of a breakdown by using an electron conducting titanium oxide as a main constituent for the conducting fine powder of a current limiting layer. CONSTITUTION:A transparent electrode 2 is formed on a glass base 1, and a light emitting layer 3 made of ZnS:Mn (0.3wt.%) is formed on it by deposition. A paint dispersed with TiO fine powder into a mixed solution of binder resin and thinner is coated on it, then the paint is dried to form a current limiting layer 4. Al is deposited on it to form a back electrode, and the back electrode is scribed with a diamond needle to form grooves 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescence (hereinafter abbreviated as EL) element, and more particularly to an EL element having an improved current limiting layer.

[0002]

2. Description of the Related Art An EL display to which an EL element is applied is one of the promising flat panel displays that are rapidly becoming popular in portable computer terminals and the like in recent years.

EL elements include thin film type EL elements and powder type E elements.
Two types of L elements are known, but recently, a hybrid EL element (Hybr) that combines a thin film type and a powder type is known.
The so-called idEL element or Composite EL element) has attracted attention as one of the promising EL elements. (For example, British Patent Publication 2176340.
No. A, British Patent Publication No. 2176341A) FIG. 3 is a view showing a cross-sectional structure of a conventional hybrid EL device. The structure and manufacturing method of a conventional EL element will be described with reference to FIG.

A transparent electrode material such as indium tin oxide (ITO) is formed as a transparent electrode 2 on the glass substrate 1 by sputtering, vacuum deposition or the like, and then formed into a predetermined shape by a method such as photolithography. Pattern. The light emitting layer 3 is formed thereon by a vacuum vapor deposition method, a sputtering method,
It is formed using a method such as MOCVD. Examples of the material for the light emitting layer include ZnS, ZnSe, CdS, and other 2-6 group compounds, transition metals such as Mn and Cu, and Tb, Sm, and D.
A rare earth element such as y, or a fluoride or chloride thereof doped with an emission center is often used. On top of that, a powder layer of several tens of μm in which conductive fine powder is hardened with an organic binder is formed as a current limiting layer 7 by a method such as a spray method. Finally, a metal such as aluminum is formed as the back electrode 5 by vacuum deposition or sputtering to form an EL element.

When manufacturing a dot matrix type EL display panel, thereafter, the back electrode and the current control layer are patterned mechanically at the same time, for example, by mechanically scratching the back electrode and the current control layer using a diamond needle or the like. .. Therefore, the thickness of the current limiting layer is 5 μm to 30 μm.
μm.

[0006] The current limiting layer 7 serves to prevent the EL element from being destroyed due to the decrease in the resistivity of the light emitting layer due to the heat generation of the EL element during the light emission. The larger the resistance of the current limiting layer is, the more stable it is against dielectric breakdown of the element, but if it is too large, the voltage drop in the current limiting layer becomes large, which leads to an increase in the drive voltage of the EL element. Naturally, there is a limit, and in the film thickness range of 5 μm to 30 μm, 50Ω to 2 per unit area (1 cm ² ) in the film thickness direction.
Resistance value of 00Ω, that is, from 1 × 10 ⁴ Ω · cm to 5 ×
It is preferable to have a resistivity of 10 ⁵ Ω · cm.

The substance of the conductive fine powder is 1 × in order to have the above-mentioned resistivity after being hardened with a binder.
It is required to have a resistivity of about 10 ⁴ Ω · cm to ⁵ × 10 ⁵ Ω · cm. Although ZnS powder coated with copper was used in the EL device of the prior art, MnO ₂ fine powder, which is black and has a good contrast of the device and whose resistance value does not change with time due to the movement of copper, has been used. Came.

[0008]

However, in the above-mentioned conventional hybrid EL device, the resistivity of the current limiting layer changes due to temperature change, which causes uneven brightness during use and shortens the service life. There was a serious problem.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, in which a transparent electrode, a light emitting layer and a conductive fine powder are used as a binder on a transparent insulating substrate. An electroluminescent device in which a current limiting layer fixed by and a back electrode are sequentially laminated, wherein an electroconductive titanium oxide is used as a main component of the conductive fine powder. is there.

The titanium oxide used in the present invention is a crucible of aluminum, molybdenum, etc.
It can be obtained by directly reacting titanium dioxide with metallic titanium at ℃ or by reducing titanium dioxide with hydrogen at a high pressure of about 130 atm and a high temperature of about 2000 ℃. The titanium oxide thus obtained is an electron conductor represented by the chemical formula TiO _n (n = 0.64 to 1.25) and has a low specific electrical resistivity. Therefore, in order to adjust the resistivity of the current limiting layer, a substance having a higher resistivity such as tungsten is mixed and used.
The particle size of the conductive fine powder is preferably 1 μm or less, and black or dark blue is preferable in order to increase the contrast of EL display.

In the current limiting layer of the EL device of the present invention, the conductive fine powder itself has a small change in resistivity with a rise in temperature, and there is substantially no change in resistance value between 300 and 400K. The resin used as a binder for solidifying conductive fine powder into a layer is not particularly limited, but examples of usable resins include vinyl resins, polyester resins, polyamide resins, and cellulose resins. , Polyurethane resins, urea resins, epoxy resins, melamine resins, silicone resins, etc.,
In particular, a resin having a polar group such as a hydroxyl group, a carboxyl group, a sulfonyl group or a nitro group, or a reactive group such as an epoxy group, an isocyanuric group or a silanol group is preferably used.

[0012]

Since the conductive fine powder of the current limiting layer of the present invention contains titanium oxide, which is an electron conductor, whose electric resistance changes little with temperature rise, as a main component, heat generation due to light emission of the EL element is suppressed, Device breakdown is prevented.

[0013]

EXAMPLES The present invention will be described below with reference to examples. Figure 1
Sectional drawing of the electroluminescent element of this invention, FIG. 2 is a figure for demonstrating the temperature dependence of the resistivity of a current limiting layer,
FIG. 3 is a cross-sectional view of a conventional electroluminescent element. Example After forming ITO as a transparent electrode 2 on a glass substrate 1 by a reactive sputtering method to a thickness of about 5000 nm,
It was patterned into a predetermined shape by the photolithography method. Subsequently, manganese (Mn) was used as the light emitting layer 3 in an amount of 0.1.
ZnS doped with 3 wt% was formed into a film by using an electron beam evaporation method of about 1 μm.

Next, a paint prepared by dispersing fine powder of titanium monoxide TiO (the composition of which is n = 1 in the above chemical formula) in a mixed liquid of a binder resin and a thinner is applied and dried by a spray method,
A current limiting layer 4 having a resistivity of 1.7 × 10 ⁵ Ω · cm and a film thickness of 10 μm was formed.

Next, as the back electrode 5, aluminum (Al) is deposited to a thickness of about 1 μm by a vacuum deposition method, and then the current limiting layer and the aluminum film are simultaneously scribed using a diamond needle to form the groove 6 A back electrode pattern having a predetermined shape separated by was formed.

When the EL device thus manufactured was connected to a driving circuit to emit light, the entire surface of the light emitting portion emitted light uniformly, and uneven brightness was not observed. In addition, the result of measuring the change in resistivity with temperature of the current limiting layer of this EL element is shown by a white circle in FIG. Reciprocal of absolute temperature 2.5 × 10 ^{-3 to} 3.25 × 10 ^-3 K ^-1 (35 to ¹
The resistivity was constant up to 27 ° C. Comparative Example MnO ₂ powder produced by the electrolysis method was crushed with a ball mill to an average particle size of 0.3 μm, and this was used as a binder resin so that the ratio of the volume of MnO ₂ powder to the volume of binder resin was 3: 7. A mixed liquid with a thinner was added and dispersed to prepare a paint.

This coating material was applied onto a glass substrate 1 having a light emitting layer 3 and a transparent electrode 2 prepared in the same manner as in the example by a spray method and dried to have a resistivity of 1.3 × 10 ⁵ Ω · cm.
Then, the current limiting layer 7 having a film thickness of 13 μm was formed.

Then, the back electrode 5 is formed in the same manner as in the embodiment.
Was formed and scribed using a diamond needle to form a predetermined back electrode pattern.

When the EL element thus manufactured was connected to a drive circuit to emit light, the temperature of the EL element increased as the applied voltage was increased to increase the luminance, and
The breakdown occurred sequentially from the brightest element in the element.

The change in resistivity with temperature of the current limiting layer of this EL device was measured in the same manner as in the example. The obtained results are shown by black circles in FIG. It was observed that the resistivity decreased with increasing temperature.

[0021]

According to the present invention, the uneven brightness of the EL element is improved and the breakdown of the EL element is prevented, so that the reliability of the EL element can be improved.

Further, in the EL device of the present invention, the resistivity of the current limiting layer is constant irrespective of temperature, so that the time variation of the required power and the time variation of the luminance are small.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an example of an electroluminescent device of the present invention.

FIG. 2 is a diagram illustrating temperature dependence of resistivity of a current control layer.

FIG. 3 is a cross-sectional view of a prior art electroluminescent device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Transparent electrode, 3 ... Light emitting layer, 4 ... Current control layer using electronically conductive titanium oxide as a main component of electroconductive fine powder, 5 ...・ Back electrode,
6 ... Groove, 7 ... Current limiting layer using MnO ₂ as conductive fine powder

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiaki Asaki 3-5-11 Doshomachi, Chuo-ku, Osaka City, Osaka Prefecture Nippon Sheet Glass Co., Ltd. (72) Inventor, Enjo Katsuhisa, Osaka City, Osaka 3-5-11 Dosyo-cho, Tokyo Inside Nippon Sheet Glass Co., Ltd.

Claims (2)

[Claims] 1. An electroluminescent device comprising a transparent insulating substrate, a transparent electrode, a light emitting layer, a current limiting layer in which conductive fine powder is fixed with a binder, and a back electrode are sequentially laminated on the transparent insulating substrate. An electroluminescent device comprising an electronically conductive titanium oxide as a main component. 2. The electroluminescent device according to claim 1, wherein the titanium oxide in the conductive fine powder is 90% by weight or more.