JPH06251875A - Electroluminescent element - Google Patents

Abstract

PURPOSE:To suppress the luminance unevenness of a emitted light and prevent the generation of a breakdown by using, as a conductive fine powder for current limiting layer, an antimony contained-thin oxide fine powder in which a specified part of thin atom is substituted by antimony atom. CONSTITUTION:A transparent electrode material such as ITO is formed as a transparent electrode 2 on a glass plate 1 by means of spattering, and a light emitting layer 3 is formed thereon by vacuum evaporation. On the layer 3, a powder layer of several 10mum formed by solidifying the conductive fine powder of a tin oxide containing 0.01-1% of antimony with an organic resin binder is formed as a current limiting layer 4 by means of spraying. A film of a metal such as aluminum is formed thereon as a back plate 5 by means of vacuum evaporation or spattering to form an EL element. Since the antimony- contained tin oxide fine powder has a temperature coefficient of electric resistance of substantially 0, the current of the layer 4 is never changed, and the luminance unevenness or life shortening of the luminescence center can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved electroluminescence (hereinafter abbreviated as EL) element. More specifically, the current limiting layer is improved so that there is no uneven brightness.
In addition, the present invention relates to a hybrid drive type EL element that can be driven by direct current so that breakdown of light emission does not occur.

[0002]

2. Description of the Related Art An EL display to which an EL element is applied is one of the promising flat displays that are rapidly becoming popular in portable computer terminals in recent years.
Is one. Two types of EL elements are known, a thin film type EL element and a powder type EL element. Recently, a mixed molding EL element in which a thin film layer and a powder layer are combined is
It has come to be noticed as one of the prominent EL elements (for example, British Patent Publications 2176340 and 21).
No. 76341).

[0003]

In the above-mentioned conventional hybrid EL device, manganese dioxide (MnO ₂ ) is used as the conductive fine powder forming the current limiting layer. In the EL element in which the current limiting layer is formed by using manganese dioxide as the conductive fine powder, the temperature of the current limiting layer rises while the EL element emits light, which lowers the electric resistance of the current limiting layer. However, a larger current than that at the time when the EL element starts to emit light comes to flow in the EL element. This causes a phenomenon that the temperature of the current limiting layer further rises, which makes it difficult for the EL element to stably emit light continuously for a long time, and this phenomenon causes uneven brightness in the EL element. . Also, when the light emission is stopped, the light is not completely extinguished and the light is not extinguished.
Afterglow was observed with the naked eye for a certain period of time, which was a cause of deteriorating the display quality as an EL display. The present invention is
It was made to solve the above problems,
It is an object of the present invention to provide an EL element in which unevenness in luminance does not occur even when light emission is continued for a long time and breakdown of the element due to an excessive current is prevented.

[0004]

According to the present invention, a transparent electrode, a light emitting layer, a current limiting layer having conductive fine powder fixed with an organic resin binder, and a back electrode are laminated in this order on a transparent electrically insulating substrate. The electroluminescent element is an electroluminescent element using antimony-containing tin oxide fine powder in which 0.01 to 1% of tin atoms are replaced with antimony atoms, as the conductive fine powder of the current limiting layer.

As the transparent electrically insulating substrate used in the present invention, a glass plate having a soda lime silica composition used for window glass, a low expansion glass (for example, Corning Glass Co., Ltd., trade name 7059), or the like is used. The transparent electrode on the electrically insulating substrate is provided by forming a film of a transparent electrode material such as tin-doped indium oxide (hereinafter referred to as ITO) by a method such as sputtering or vacuum deposition.
The materials used for the light emitting layer of the present invention are ZnS, ZnSe, C
Illustrative examples include those in which a 2-6 group compound such as dS is doped with a transition metal such as Mn or Cu or a rare earth element such as Tb, Sm, or Dy or a fluoride or chloride thereof as an emission center, and the light emitting layer is vacuum. Vapor deposition method, sputtering method, MOC
It can be provided using a method such as the VD method.

The current limiting layer of the present invention contains 0.01 atom of tin atoms.
It is formed by fixing antimony-containing tin oxide fine powder in which ˜1% is replaced with antimony atoms, fixed by an organic resin binder. Examples of the organic resin binder that can be used in the current limiting layer of the present invention include vinyl resins, polyester resins, polyamide resins, cellulose resins, polyurethane resins, urea resins, epoxy resins, melamine resins, Examples of the silicone resin include organic resins having a polar group such as a hydroxyl group, a carboxyl group, a sulfonyl group, and a nitro group, or a reactive group such as an epoxy group, an isocyanuric group, and a silanol group. . The tin oxide fine powder used in the present invention has a resistivity of about 1 × 10 ³ Ωcm to which only the tin oxide fine powder is hardened into a tablet shape by applying a pressure of about 100 kg / cm ^2.
It shows about 2 × 10 ⁵ Ωcm. When the resistance value of the current limiting layer of the present invention increases, the risk of element destruction due to overcurrent flowing decreases, but the voltage drop in the current limiting layer increases and the voltage required to drive the element increases. Therefore, from both characteristics, the current limiting layer has a thickness of 5 μm to 3 μm.
The resistance value is preferably 0 μm and a resistance value of 10 Ω to 2000 Ω per unit area (1 cm ² ) in the thickness direction. Therefore, the resistivity of the current limiting layer is preferably about 1 × 10 ⁴ Ωcm to about 2 × 10 ⁶ Ωcm.

The particle size of the tin oxide fine powder used in the current limiting layer of the present invention is preferably 1 μm or less, more preferably 100 nm or less. In particular, when tin oxide fine particles mainly containing a particle size of 100 nm or less are used, the current limiting layer becomes transparent to visible light. Therefore, if a transparent electrode is used as the back electrode, light emission can be extracted from the back electrode side. The antimony-containing tin oxide fine powder of the present invention can be obtained by a known method of precipitating a precipitate by hydrolysis of chlorides and oxychlorides of tin and antimony, and then calcining.

The ratio of the antimony-containing tin oxide fine powder to the organic resin binder is expressed by the volume ratio occupied in the current limiting layer: fine powder / organic resin binder = 0.4-
It is preferably within the range of 2.5. The ratio is 0.4
If it is smaller than 1, the resistance of the current limiting layer increases, and
If it is larger than 5, the stability of the layer such as cracks in the current limiting layer is deteriorated, which is not preferable. As a specific method of providing the current limiting layer on the light emitting layer, a mixture of antimony-containing tin oxide fine powder and an organic resin binder, or a mixture of a sol and a binder solution in which antimony-containing tin oxide fine particles are dispersed in water or an organic solvent is used. Is applied, for example, by spraying. The back electrode of the present invention is provided by depositing a metal such as aluminum (Al) by vacuum deposition or sputtering. Then, in order to secure the humidity resistance of the EL element, the element can be sealed with a cover glass that covers the back electrode.

Further, the antimony-containing tin oxide fine powder for use in the current limiting layer of the EL device of the present invention is made to mainly contain particles having a particle size of 100 nm or less so as to be transparent to visible light, and the back surface thereof. Known ITO for electrodes
By using a transparent conductive material such as (indium oxide doped with tin) or tin oxide, it is possible to obtain an EL element in which light emission can also be extracted from the back electrode. At this time, in order to increase the ratio of the light emitted to the back electrode side in the light emission generated in the light emitting layer, the transparency of the transparent electrode provided on the electrically insulating substrate is reduced or made opaque, so that the light emission is caused by the electrical insulation. It is better to prevent it from going out through the flexible substrate. As described above, the EL element in which the emitted light is emitted only from the back electrode side is used for sealing the laminate forming the EL element by covering the back electrode in order to secure the moisture resistance of the element. If a glass plate is provided and a color filter made of an organic dye or organic pigment is provided on the inner surface or the outer surface of the glass plate according to the shape of the back electrode or directly on the back electrode surface, multicolor display with high brightness is possible. It can be an EL element.

[0010]

The antimony-containing tin oxide fine powder used in the current limiting layer of the EL device of the present invention is electronically conductive, and its temperature coefficient of electric resistance is almost zero. Therefore, even if the temperature of the current limiting layer rises due to heat generated when the EL element is emitting light, a constant current flows through the EL element without changing the electric resistance of the current limiting layer. The electric resistance of the limiting layer decreases, and a larger current flows,
As a result, the disadvantage of the conventional EL that the temperature further rises is solved. As a result, it is possible to suppress uneven brightness and shorten the life of the EL element during light emission. In addition, the afterglow of the light emission pattern that occurs when the light emission is stopped will not be seen.

The tin oxide fine particles used in the present invention include
The electric resistivity of the fine particles is adjusted by substituting 0.01 to 1% of tin atoms with antimony atoms, so that the electric resistivity of the current limiting layer mixed and fixed with the organic resin binder can be optimally adjusted. it can.

[0012]

1 is a cross-sectional view showing a laminated structure of an embodiment of a hybrid EL device of the present invention. FIG. 2 is a sectional view showing a laminated structure of another embodiment of the hybrid EL device. The hybrid EL device of the present invention will be described with reference to FIG. Glass substrate 1
A transparent electrode material such as ITO is deposited as a transparent electrode 2 on the upper surface by a method such as sputtering or vacuum deposition. The light emitting layer 3 is formed thereon by a method such as a vacuum vapor deposition method, a sputtering method, or a MOCVD method. On the light emitting layer 3, a powder layer of several tens of μm in which tin oxide conductive fine powder containing 0.01 to 1% of antimony is hardened with an organic resin binder as a current limiting layer is formed by a method such as a spray method. Membrane and harden. Then, a metal such as aluminum (Al) is formed as a back electrode on the current limiting layer by vacuum deposition or sputtering to form an EL element. When manufacturing a dot matrix type display panel, it is preferable that the back electrode and the current limiting layer are mechanically scratched using a diamond needle or the like to simultaneously perform patterning of the back electrode and the current limiting layer. In order to perform pattern processing by such a method, the thickness of the current limiting layer is preferably in the range of 5 μm to 30 μm. The current limiting layer 4 and the back electrode 5 of FIG.
Shows the cross-sectional shape after the stripe-shaped pattern processing is performed by scratching in the direction perpendicular to the paper surface. If necessary, this EL element is sealed with resin or glass to take a moisture resistance prevention measure.

Example 1 ITO was formed as a transparent electrode 2 on a glass substrate 1 to a thickness of about 500 nm by a reactive sputtering method, and then formed into a stripe shape in a direction parallel to the paper surface by a photolithography method. It was patterned. Subsequently, ZnS doped with 0.3% by weight of manganese (Mn) was used as the light emitting layer 3.
Was deposited to a thickness of about 1 μm using an electron beam evaporation method. Next, the volume ratio after solidification of the tin oxide fine powder containing antimony substituted by 0.5 atom% with respect to the tin atom and the polyester binder resin (trade name TP-249 manufactured by Nippon Gohsei) is 4 to 6. Add a mixture of binder resin and thinner and a small amount of black pigment, stir in a bead mill for 1 hour, filter with a 10 μm Teflon membrane filter, then paint with a spray method using a 5 μm Teflon membrane filter. , Dried, resistivity 1 × 1
A current limiting layer having a thickness of 0 ⁵ Ωcm and a thickness of 10 μm was formed. The produced current limiting layer was a black layer having no voids and fixed by a resin binder and having a substantially uniform thickness.

Next, an Al film is formed as a back electrode by vacuum evaporation to a thickness of about 1 μm, and then the current limiting layer and Al are formed.
The striped back electrode 5 was formed by simultaneously scribing the film using a diamond needle. The layered structure of the EL device thus manufactured is shown in FIG. When this EL element was connected to a DC drive circuit to emit light, it uniformly emitted light, and no uneven brightness was observed.

Example 2 As shown in FIG. 2, a tantalum metal film which is opaque to visible light is formed as a electrode 2A on a glass substrate 1 by sputtering to a thickness of about 500 nm, and then photolithography. It was patterned into a predetermined shape by the method. Subsequently, a ZnS layer of about 1 μm doped with 0.3% by weight of Mn was formed as a light emitting layer 3 on the electrode 2A by a sputtering method. Next, 0.3 atom% of antimony with respect to tin atom
A bead mill in which a mixed liquid of a resin binder and a thinner was added so that the volume ratio after solidification of the tin oxide fine powder contained by substitution and the polyester binder resin (trade name TP-249 manufactured by Nippon Gohsei) became 5: 5. Stir for 1 hour at 10
Filter with μm Teflon membrane filter, then 5μ
The paint obtained by filtering with a m-Teflon membrane filter is applied by a spray method and dried to obtain a resistivity of 2 × 10.
A current limiting layer having a thickness of ⁵ Ωcm and a thickness of 15 μm was formed. The produced current limiting layer was a colorless and transparent layer having no voids and fixed by a resin binder and having a substantially uniform thickness.

Next, as a back electrode, a film of ITO having a thickness of about 1 μm is formed by a sputtering method, and then the above current limiting layer and I are deposited.
The TO film and the TO film are simultaneously scribed using a diamond needle to form a stripe-shaped back electrode 5 arranged in a direction perpendicular to the paper surface as shown in FIG. 2, and the ITO back surface patterned in the stripe shape is formed. A transparent coloring substance (color filter) containing an organic pigment as a coloring component was formed on the transparent electrode by a known electrodeposition method. Every other color filter is red (shown as R in FIG. 2),
It was provided so as to be green (shown by G in FIG. 2). The obtained EL device was connected to a DC drive circuit, and every other voltage was alternately applied to the back electrode 5 to cause light emission. As a result, a multicolor EL device in which red and green were alternately and uniformly emitted was obtained. . In addition, uneven brightness was not observed. Here, in the current limiting layer of the EL device manufactured in the above-mentioned Examples 1 and 2,
The change in electrical resistivity with temperature was measured. 36 ° C (10
00 / absolute temperature corresponds to 3.24) to 171 ° C (100
The measurement result in the temperature range of 0 / absolute temperature corresponds to 2.25) is shown in FIG. As is clear from FIG. 3, the resistivity of the current limiting layers of Example 1 and Example 2 showed a substantially constant value regardless of temperature.

Example 3 A tantalum metal film which is opaque to visible light is used as an electrode 2 on a glass substrate 1 by a sputtering method to have a thickness of about 500 nm.
After being formed into a film having a thickness of 1, the film was patterned into a predetermined shape by a photolithography method. Then, as the light emitting layer 3, M
ZnS doped with 0.3% by weight of n was formed into a film by a sputtering method of about 1 μm. Next, a sol in which a tin oxide fine powder containing 0.3 atom% of antimony substituted for tin atoms is dispersed in dimethylacetamide is used as a fine powder and a polyester resin binder (trade name TP-24 manufactured by Nippon Synthetic Co., Ltd.).
Prepare a mixture solution diluted with thinner so that the volume ratio after solidification of 9) becomes 5: 5, stir this solution with a bead mill for 1 hour, filter with a 10 μm Teflon membrane filter, and then a 5 μm Teflon membrane filter. To obtain a paint, which is applied onto the light emitting layer by a spray method and dried, and the resistivity is 1 × 10 ⁵ Ωcm and the film thickness is 15
A μm current limiting layer was formed. The produced current limiting layer was a colorless and transparent layer having almost no uniform thickness, which was fixed by the resin and had no voids.

Next, an ITO film is formed as a back electrode by sputtering to a thickness of about 1 μm, and then the current limiting layer and the ITO film are formed.
The film was simultaneously scribed with a diamond needle to form a striped back electrode pattern as in Example 2. A multicolor EL device having a laminated structure shown in FIG. 2 in which red and green color filters (transparent colored films) are alternately provided on the ITO back electrode patterned in the stripe shape by alternate electrodeposition. Got When this EL element was connected to a DC drive circuit and a voltage was alternately applied to every other back electrode to cause light emission, an EL element in which red and green were alternately and uniformly emitted was obtained.
In addition, uneven brightness was not observed.

Comparative Example Manganese dioxide (MnO ₂ ) powder produced by the electrolysis method was crushed with a ball mill to an average particle size of 0.3 μm, and the volume of the MnO ₂ powder and a resin binder (manufactured by Nippon Zeon, trade name MR-110) were used. ) Was mixed with the solvent so that the volume ratio thereof was 3 to 7, and the resulting solution was prepared by using a thinner as a solvent, filtered through a 10 μm Teflon membrane filter in the same manner as in Example 1, and then filtered through a 5 μm Teflon membrane filter. A paint was made. Similar to Example 1, this coating material was applied by a spray method onto a laminate of the transparent electrode 2 and the light emitting layer 3 formed on a glass substrate and dried to obtain a resistivity of 5
A current limiting layer having a film thickness of 20 μm was formed at × 10 ⁴ Ωcm. Next, a back electrode was formed in the same manner as in Example 1 and scribed with a diamond needle to form a predetermined back electrode pattern. When the obtained EL device was connected to a DC drive circuit to emit light, the temperature of the panel increased as the brightness was increased, and breakdowns occurred sequentially from the brightest device in the panel. FIG. 3 shows the results of measuring the change in resistivity with temperature of the current limiting layer of this EL element, as in the case of the example. There was a change in resistivity of about one digit in the above temperature range.

It can be seen from FIG. 3 that the resistivity of the current limiting layer of the above example has less temperature dependence than that of the current limiting layer of the comparative example, and that the characteristic affects the luminance characteristic of the EL element. There was found.

[0021]

According to the present invention, tin oxide having a low temperature dependence of electric resistivity is fixed to a current limiting layer by a resin binder, and a predetermined amount of tin atoms is converted to antimony in tin oxide. By including it by substituting it, the electric resistivity of the current limiting layer is optimized. As a result, it was possible to obtain an EL element in which unevenness in the luminance of light emission was suppressed and breakdown did not occur.

[Brief description of drawings]

FIG. 1 is a cross-sectional view for explaining a laminated structure of an example of an EL device of the present invention.

FIG. 2 is a cross-sectional view for explaining a laminated structure of another embodiment of an EL element.

FIG. 3 is a diagram showing a change in resistivity of a current limiting layer with temperature.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Transparent electrode, 2A ... Opaque electrode, 3 ... Light emitting layer, 4 ... Current limiting layer, 5
... Back electrode, 7 ... Color filter

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shunji Wada 3-5-11 Doshomachi, Chuo-ku, Osaka-shi, Osaka Inside Nippon Sheet Glass Co., Ltd.

Claims (2)

[Claims] 1. An electroluminescent device comprising a transparent electrically insulating substrate, a transparent electrode, a light emitting layer, a current limiting layer in which conductive fine powder is fixed with an organic resin binder, and a back electrode, which are laminated in this order. An electroluminescent device, characterized in that, as the conductive fine powder of the layer, an antimony-containing tin oxide fine powder in which 0.01 to 1% of tin atoms are substituted with antimony atoms is used. 2. The conductive fine powder is fixed within a range of 0.4 to 2.5 of conductive fine powder / organic resin binder, expressed as a volume ratio in the current limiting layer. The electroluminescent element according to claim 1, wherein: