JPH05159880A - Electroluminescence element - Google Patents

Abstract

PURPOSE:To make any dielectric breakdown in an element hard to occur by farming conductive fine powder into the extent of impalpable powder of ferric oxide or the main ingredient, and reducing a temperature coefficient of electric resistivity. CONSTITUTION:In this electroluminesence element, plural pieces of striped electrodes 2 installed on top of a glass substrate 1 in a direction parallel with a paper face are installed being electrically insulated. In action, a luminescent layer 3 is installed almost over the whole surface of the glass substrate 1 so as to cover a part of the transparent electrodes 2 and a part of the exposed part of the glass substrate 1. Then plural striped current limiting layers 5 and back plates 5 are installed in a direction vertical to the paper face, and conductive fine powder is formed with impalpable powder of ferric oxide chiefly. Since this current limiting layer 4 is small in a temperature coefficient of electric resistivity, if the electro-luminescent element is driven for hours, the electrical resistivity will in no case be lower so largely even if a temperature of the element goes up. With this constitution, a large current is checked to flow into the element, and any possible dielectric breakdown in the element is thus prevented from occurring.

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 used for displaying characters, graphics, etc., and more specifically, it is a thin film-powder mixed molding that has no uneven brightness and is less likely to cause breakdown. Related to the EL element.

[0002]

2. Description of the Related Art An EL display using an EL element is rapidly spreading in portable computer terminals and workstation terminals in recent years as a display for displaying characters and graphics with high display quality. is there.

For an EL element capable of displaying characters, graphics, etc., an AC thin film type EL element having a structure in which a thin light emitting layer is sandwiched between electric insulating layers, and electrodes are provided on both outer sides of the electric insulating layer, and sulfurization Two DC powder type EL devices having a structure in which a light emitting layer made of zinc powder and a current limiting layer made of zinc sulfide powder coated with copper (Cu) on the surface and provided adjacent to the light emitting layer are sandwiched between electrodes. The type is known and put to practical use. However, recently, EL with high cost performance that can achieve excellent display quality at low cost
As a device, there is a thin film-powder mixed molding EL device (hereinafter referred to as a mixed molding EL device) in which a thin film type light emitting layer and a powder dispersion type current limiting layer are combined, and British Patent Publication 2176341.
No. A is disclosed.

According to the above-mentioned prior art, manganese dioxide fine particles hardened with an organic resin are used as the current limiting layer, and the electric resistivity of the current limiting layer is 1 × 10 ^{4 to} 5 ×.
It is set to 10 ⁵ Ωcm.

[0005]

However, in the above-mentioned conventional hybrid EL device, since the electric resistivity of the current limiting layer has a negative temperature coefficient, the temperature of the device is increased by driving the EL device. Then, the electrical resistivity of the current limiting layer is lowered, which causes an excessive current to flow, and thus the current limiting layer is likely to be broken down. This phenomenon has been a serious drawback for EL devices, which shortens the life of the EL device. In addition, when displaying, uneven brightness is likely to occur. The present invention has been made in order to solve the problems of the above-described prior art, and therefore provides an EL element in which breakdown of the current limiting layer is unlikely to occur and uneven brightness is less likely to occur.

[0006]

The present invention has been made in the process of researching a fine powder material used for a current limiting layer in order to solve the above problems. Layer, a current limiting layer formed by solidifying conductive fine powder with an organic resin, and a back electrode in this order, wherein the conductive fine powder is mainly composed of ferric oxide. It is an element.

In the current limiting layer of the EL element of the present invention, the rate of change of the electric resistivity of the current limiting layer is suppressed to a small value even if the element temperature rises due to the light emission of the EL element.

The conductive fine powder used in the current limiting layer according to the present invention contains ferric oxide as a main component. When the fine powder used is only ferric oxide, the electric resistivity of the current limiting layer has a small negative temperature coefficient. Further, as the fine powder used, ferric oxide may be mixed with a small amount of another metal oxide. Other metal oxides used as a minor component include ferrous oxide (FeO), ferrous manganese oxide (MnO), cobaltous oxide (CoO), nickel oxide (NiO), cuprous oxide (CuO). ), Zinc oxide (ZnO), lead oxide (PbO), strontium oxide (Sr0), and the like. These metal oxides are
The current limiting layer may be contained in a range that does not increase the temperature coefficient. In the present invention, the change in the electrical resistivity in the temperature range of 307 to 400K is included within the range of 40% or less. Further, in order to make the change in the electrical resistivity in the temperature range of 307 to 400 K to be a small value of about 20% or less,
The content of the metal oxide mixed as a small amount component is preferably less than 20%.

When using two kinds of fine powders of ferrous manganese oxide and ferric oxide, it is possible to use fine powders obtained by mixing and pulverizing these metal oxides and heating them to a high temperature.

The fine powder particles of the current limiting layer used in the present invention are electron conductors, which are uniformly dispersed in the organic resin and have an electric resistivity of 1 × 10 ^{4 to} 5 × 10 ⁵ Ωcm. It is said that. The electric resistivity of the current limiting layer is 1 × 10 ⁴ Ωc
If it is smaller than m, the resistance value occupied by the light emitting layer determines the resistance value of the entire device, which is not preferable. Further, if the electric resistivity is larger than 5 × 10 ⁵ Ωcm, the voltage drop in the current limiting layer becomes large and the driving voltage for driving the EL element must be increased, which is not preferable. The electrical resistivity of the current limiting layer is preferably in the above range and the thickness thereof is preferably 5 to 30 μm. At this time, the current limiting layer has a thickness of 50 to 200 Ω / cm 2 in the film thickness direction. In addition, it is preferable that the particle size of the conductive fine powder used for the current limiting layer does not exceed 1 μm in order to suppress unevenness in light emission. Further, in order to increase the display contrast of the EL element, ferric oxide or ferric oxide is used. It is preferable to use a black or dark blue metal oxide such as 1 Titanium.

The organic resin used as the binder of the conductive fine powder of the current limiting layer of the EL device of the present invention is not particularly limited, but vinyl-based resin, polyester-based resin, polyamide-based resin, cellulose resin, polyurethane-based resin. Examples include resins, urea-based resins, epoxy-based resins, melamine-based resins, silicone-based resins, etc., but especially reactions of polar groups such as hydroxyl groups, carboxyl groups, sulfonyl groups, nitro groups, epoxy groups, isocyanuric groups, silanol groups, etc. Those having a group are preferably used.

As the transparent insulating substrate of the present invention, a glass plate having an alkali-free composition containing almost no sodium component, a low expansion glass plate having a small volume expansion coefficient containing silica and alumina components, a quartz glass plate, and a soda-lime glass plate. The one coated with a silica film is used.

As the transparent electrode of the present invention, a tin-doped indium oxide (ITO) film or tin oxide patterned into a predetermined shape by a method such as photolithography is used.

The light emitting layer according to the present invention includes zinc sulfide (ZnS), zinc selenide (ZnSe), calcium sulfide (CaS), strontium sulfide (SrS) and the like.
-6 Group compounds, transition metals such as manganese (Mn) and copper (Cu), and rare earth elements such as terbium (Tb), samarium (Sm), dysprosium (Dy), europium (Eu), and cerium (Ce), or the like. What is doped with the fluoride, chloride or the like as an emission center is used.

[0015]

Since the current limiting layer of the present invention has a small temperature coefficient of electric resistivity, the electric resistance of the current limiting layer is greatly reduced even when the temperature of the EL element is increased by driving the EL element for a long time. There is no. Therefore, the phenomenon that a large current flows through the element due to the decrease in the electric resistance of the current limiting layer is suppressed, and as a result, the dielectric breakdown of the EL element is prevented.

[0016]

EXAMPLES The present invention will be described in detail below based on examples. FIG. 1 is a partial cross-sectional view of one embodiment of the electroluminescent element of the present invention, and FIG. 2 is a diagram showing the temperature dependence of the electrical resistivity of the current limiting layer. EL shown in FIG.
The device is provided with a plurality of stripe-shaped transparent electrodes 2 provided on a glass substrate 1 in a direction parallel to the paper surface while being electrically insulated from each other. Further, a light emitting layer 3 is provided in a part of the transparent electrode 2 and the glass. The glass substrate 1 is provided on almost the entire surface so as to cover a part of the exposed portion of the substrate 1, and a plurality of stripe-shaped current limiting layers 4 and back electrodes 5 are provided in a direction perpendicular to the plane of the drawing. Then, a DC pulse voltage is applied between the back electrode 5 and the transparent electrode 2 by the power source 6 to drive the same.

A method of making this EL element will be described below. A transparent electrode material such as indium tin oxide (ITO) is coated as a transparent electrode 2 on the glass substrate 1 by sputtering, vacuum deposition, or the like, and then patterned into a predetermined shape by a method such as photolithography. Next, the light emitting layer 3 is formed by a method such as a vacuum vapor deposition method, a sputtering method, or a MOCVD method. Then, on the light emitting layer 3, a powder layer having a thickness of several tens of μm in which conductive fine powder is hardened with an organic resin is formed as a current limiting layer 4 by a method such as a spray method. Finally, a metal such as aluminum (Al) is coated as the back electrode 5 by vacuum deposition or sputtering. After that, the back electrode 5 and the current limiting layer 4 are simultaneously scratched by a method perpendicular to the paper surface using a diamond needle or the like to form a back electrode having a predetermined shape. By the above, a dot matrix type EL element can be obtained. Example 1 ITO having a thickness of about 500 nm was used as a transparent electrode on a transparent glass substrate (trade name 7059 glass manufactured by Corning Incorporated).
Was coated by a reactive sputtering method, and then a transparent electrode having a predetermined shape was prepared by a photolithography method. continue,
As a light emitting layer, a ZnS film doped with 0.3% by weight of Mn was coated by an electron beam evaporation method of about 1 μm while maintaining the heating temperature of the glass substrate at 200 ° C. Then, the light emitting layer was annealed in vacuum at 550 ° C. for 2 hours. Next, the volume ratio of fine powder of ferric oxide to epoxy resin is 3:
7 was mixed with a thinner to prepare a paint in which fine powder was uniformly dispersed in the resin. This paint is applied by a spray method and dried to obtain an electric resistivity of 2.7 × 10 ⁵ Ωc.
and a thickness of 10 μm for a current limiting layer. Further, aluminum having a thickness of 1 μm is coated as a film for the back electrode by an electron beam vapor deposition method, and then a film for the current limiting layer and the back electrode are simultaneously scribed by using a diamond needle to form a stripe shape of a predetermined shape. The back electrode of was prepared. Finally, the entire EL element was covered with a cover glass, and the light emitting portion of the EL element was sealed with an organic resin to take measures against humidity.

The sample 1 of the EL device thus obtained was connected to an EL drive circuit for applying a pulse voltage of 100 V, and after the light was emitted for 100 hours, the light emitting surface was observed. No unevenness was observed.

When the temperature dependence of the electric resistance of the current limiting layer used in Sample 1 was measured, the characteristics shown by the white circles in FIG. 2 were obtained. The numerical value expressed by 1000 / absolute temperature (K) was 2.50 to 3.25, that is, the change in electrical resistivity was 12% in the temperature range of 308 to 400K, which was a small change rate. The results of the light emission test are shown in Table 1. Example 2 An EL device sample 2 was prepared in the same manner as in Example 1 except that the conductive fine powder for the current limiting layer was changed to the material shown in Table 1. The results obtained are shown in Table 1.

[0020]

[Table 1]

Example 3 Sample 3 of an EL device was prepared in the same manner as in Example 1 except that the conductive fine powder for the current limiting layer was changed to the material shown in Table 1. The results obtained are shown in Table 1. The rate of change of the electrical resistivity of the current limiting layer of Sample 3 showed a negative value. Comparative Example The conductive fine powder of the current limiting layer was mixed using a thinner so that the volume ratio of the manganese dioxide having an average particle size of 0.3 μm and the epoxy resin produced by the electrolysis method was 3: 7, A paint in which manganese was uniformly dispersed in an epoxy resin was prepared. Using this coating solution, a comparative sample of an EL device was prepared in exactly the same manner as in Example 1 except that a current limiting layer having a thickness of 13 μm and an electric resistivity of 1.3 × 10 ⁵ Ωcm was used.

The comparative sample of the obtained EL device was connected to an EL drive circuit for applying a pulse voltage of 100 V, and light was emitted for 50 hours. As the brightness was increased, the temperature of the EL element was increased, and breakdown was sequentially generated from the brightest part of the light emitting surface, and that part became a black spot.

When the temperature dependence of the electric resistance of the current limiting layer used in Comparative Sample 1 was measured, the characteristics shown by the black circles in FIG. 2 were obtained. The value expressed by 1000 / absolute temperature (K) is a temperature of 2.50 to 3.25, that is, 308 to
In the temperature range of 400 K, the electrical resistivity decreased with increasing temperature, and in the above temperature range, the change rate was 91%, that is, about one digit change.

From the above test results, when the conductive fine powder used for the current limiting layer contains ferric oxide as a main component and the electric resistance of the current limiting layer changes little with temperature, breakdown of the device occurs. I find it difficult.

[0025]

According to the present invention, uneven brightness is improved,
In addition, it is possible to obtain an EL element in which insulation breakdown of the element is unlikely to occur. Further, according to the present invention, it is possible to obtain the EL element in which the fluctuation of the required power with time is small and the deterioration of the luminance is small.

[Brief description of drawings]

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

FIG. 2 is a diagram showing the temperature dependence of the electrical resistivity of the current limiting layers used in Examples and Comparative Examples.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Transparent electrode, 3 ... Emitting layer, 4 ... Current limiting layer formed by solidifying conductive fine powder, 5 ...
・ Back electrode, 6 ... Driving power supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunji Wada 3-5-11 Doshumachi, Chuo-ku, Osaka-shi, Osaka Within Nippon Sheet Glass Co., Ltd. (72) Inventor Katsuhisa Enjoji 3-chome, Dosho-machi, Chuo-ku, Osaka 5th-11th Nippon Sheet Glass Co., Ltd.

Claims (2)

[Claims] 1. A transparent electrode, a light emitting layer, and a transparent insulating substrate.
In an electroluminescent element in which a current limiting layer obtained by solidifying conductive fine powder with an organic resin and a back electrode are sequentially laminated, the conductive fine powder is mainly composed of fine powder of ferric oxide. .. 2. The electroluminescent device according to claim 1, wherein the conductive fine powder contains 80 wt% or more of fine powder of ferric oxide.