JPH0744072B2 - EL device and manufacturing method thereof - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an EL (electroluminescence) device used for flat displays and surface light sources, and a method for manufacturing the same.

(Prior art and its problems) When a voltage is applied to a fluorescent substance, it emits light.
Since the discovery of so-called electroluminescence in 1936, much research and development has been conducted with the aim of applying it to surface light sources and display devices. Various EL element configurations have been proposed and studied, but at the present time, AC-driven thin film EL elements in which an insulator thin film is inserted have excellent brightness characteristics and stability and are put to practical use as various displays. Typical 2 in Figure 2
The basic structure of a heavy insulation type thin film EL element is shown (S.I.D.74.Digest of Technical Pavers)
84 pages, SID74 diaest of tcchnical papers). A transparent electrode 22 such as ITO or a NES film, a thin film first insulator layer 23, a thin film light emitting layer 24 made of a fluorescent thin film exhibiting electroluminescence such as ZnS: Mn on a transparent glass substrate 21, and a thin film thereon. It has a multi-layered thin film structure including a second insulator layer 25 and a back electrode 26 such as an Al thin film. The first and second insulator layers are Y ₂ O ₃ and Ta ₂ O
₅ , a transparent dielectric thin film of Al ₂ O ₃ , Si ₃ N ₄ , BaTiO ₃ , SrTiO _3, etc., which is formed by sputtering or vapor deposition.
Such an insulator layer limits the current flowing in the light emitting layer,
It contributes to the stability of the operation of the EL element and the improvement of the light emission characteristics, and protects the light emitting layer from the contamination of moisture and harmful ions, and improves the reliability of the EL element. However, there are some practical problems with such a device. That is, it is difficult to eliminate the dielectric breakdown of the device over a wide area, and the yield is low, and the driving voltage applied to the device required for light emission is high because the voltage is divided and applied to the insulating layer. That is. With respect to the above-mentioned problem of dielectric breakdown of the element, it is required to adopt an insulating layer material having a good dielectric strength characteristic. Further, regarding the light emission drive voltage, it is preferable to increase the capacity of the insulating layer as much as possible in order to reduce the divided amount of the voltage applied to the insulating layer. Further, according to the operating principle of such an AC drive type EL element, the current flowing in the light emitting layer that contributes to light emission is almost proportional to the capacity of the insulator layer. Therefore, it is important to increase the capacity of the insulator layer in order to reduce the driving voltage and increase the emission brightness. That is, as the insulator layer, one having a high dielectric breakdown voltage and a large capacitance is required. From this point of view, the dielectric constant (ε) × dielectric breakdown electric field (Eb.d) is widely adopted as an index of the goodness of the insulating layer material. This ε · Eb.d. Value is practically necessary to be at least about three times the ε · Eb.d. Value of the ZnS light emitting layer (about 1.3 μc / cm ² ).・
E-Transactions on Electron De Haiths IEEE Trans Electron Devices ED-24, p903
(1977). If Eb.d. is a very large insulator material, ε
Even if the size is small, it is possible to realize a large capacity of the insulator layer by using it with a very thin film thickness, but in reality, adhesion of minute dirt and fine particles over a wide area required for display devices and surface light sources. It is extremely difficult to eliminate such defects, and the adoption of a thin insulator layer of several hundreds of liters or less is invincible. From such a point of view, adoption of a thin film having a high dielectric constant has been studied. For example, low-voltage driving has been attempted by using a PbTiO ₃ film formed by a sputtering method as an insulator layer. (IEE Transactions on Electron DeHais, IEEE Trans Electron Devices ED-28, p698
(1981)) PbTiO ₃ sputtered film has a maximum relative dielectric constant of 190 of 0.5.
Although it has a withstand voltage of MV / cm, it is not practical because the substrate temperature at the time of forming the PbTiO ₃ film requires a high temperature of about 600 ° C. Further, a SrTiO ₃ film formed by sputtering is known as a thin film showing a relatively good ε · Eb.d. Value (Japan Display-'83, Japan Display-'83, p76 (1983)). SrTiO ₃
The relative permittivity of the sputtered film is 140, and the breakdown voltage is 1.5-2 MV / c.
m and the ε · Eb.d. value is 19 to 25 μc / cm ² . This is PbT
It is superior to the ε · Eb.d. value of iO ₃ · 7 μc / cm ² . However, the SrTiO ₃ film also requires a high substrate temperature of 400 ° C. at the time of film formation, and has practical problems such as blackening by reducing the ITO transparent electrode during sputtering film formation. In addition to the drawback that the adhesion to the ZnS light emitting layer is weak, thin-film EL devices that employ these relatively high-dielectric-constant insulator layers leave minute breakage holes when dielectric breakdown occurs. It is not a self-healing type destruction that completes destruction, but there is a strong tendency to be a propagation type destruction that is fatal in practical use.

As described above, it is practically difficult to realize low voltage driving, high brightness, light emission characteristics, and stability against dielectric breakdown by adopting an insulator thin film layer having a large dielectric constant and ε · Eb.d. is there.

In addition, it is necessary to use a glass substrate that is alkali-free and expensive with a high softening point for the heat treatment process to improve the stability and characteristics of the EL device, which is also a cause of the high cost of the thin film EL device. Has become. Even if such expensive glass is adopted, it is necessary to limit the process temperature to 600 ° C or lower. In addition, the specific resistance of the ITO film used as the transparent electrode is not sufficiently small, and if the ITO film is thickened, dielectric breakdown is likely to occur at the edge part.
It was necessary to reduce the thickness to about 0.2 micron or less, and the electrode resistance could not be made sufficiently small, which was an obstacle to the realization of a display having a larger area and a larger display capacity.

As described above, the conventional thin film EL element is expensive in the constituent material, has a low yield, and requires an expensive drive circuit with a high withstand voltage, and thus the display apparatus is inevitably expensive. Also, it was difficult to increase the area.

(Object of the Invention) As described above, an EL element which emits high brightness with high reliability and low voltage driving, which solves various drawbacks of a thin film EL element formed of a multilayer thin film on a conventional glass substrate, and its It is an object of the present invention to provide a manufacturing method.

(Structure of the Invention) According to the present invention, a laminated ceramic manufactured by a green sheet method having a structure in which a ceramic substrate, a thick film electrode formed in a predetermined pattern, and a first insulator layer of a high dielectric constant ceramic are laminated. A structure in which a thin film light emitting layer of ZnS: Mn, ZnS: TbF ₃ , ZnS: SmF _3, etc., a thin second insulating layer, a transparent electrode made of a transparent conductive film such as ITO is laminated on the structure, or An EL device having a structure in which the thin second insulator layer is omitted in the structure is obtained. The laminated ceramic structure is made of a composite perovskite containing Pb as the first insulating layer, and is 1000 ° C.
The following method for manufacturing an EL element manufactured by low temperature firing is obtained.

(Detailed Description of Configuration) FIG. 1 shows the basic structure of the EL device of the present invention. EL of the present invention
The element is a laminated ceramic structure composed of a ceramic substrate 11, a thick film first electrode 12, and a high dielectric constant ceramic first insulator layer 13, and a thin film light emitting layer 14 formed by vacuum deposition, sputtering, CVD or the like. It has a basic structure composed of two insulator layers 15 and a transparent second electrode 16. A single insulating structure in which the thin film second insulator layer is omitted may be used. The light emitting layer and the second insulating layer are the same as those of a normal thin film EL element, and the EL element of the present invention is essentially a laminated ceramic in which the substrate, the first electrode, and the first insulating layer are formed by laminating and firing green sheets. The structure is characterized in that the first insulator layer is composed of a high dielectric constant material. Further, it is characterized in that the first insulating layer is made of a composite perovskite material containing Pb and is manufactured by a low temperature firing process.

The EL element of the present invention is used by observing the display from the transparent electrode side sequentially laminated on the ceramic substrate, and unlike the one using a normal glass substrate, the ceramic substrate, the first electrode, the The 1-insulator layer does not need to be translucent, and it is preferable that the 1-insulator layer is deeply colored for the effect of increasing the contrast of display.

The laminated ceramic structure as described above is manufactured by a usual green sheet laminating technique. That is, a green sheet is manufactured by mixing a ceramic raw material powder as a base material with a binder and forming a slurry and casting film. The first electrode, which is an internal electrode of ceramic, is printed on the green sheet by a screen printing method or the like. Further, by the same process, a green sheet to be the first insulator layer is prepared using a high dielectric constant dielectric material as a raw material. The thick film printing of the first electrode may be performed by printing on the green sheet. The above base part and the first
A green sheet to be an insulating layer is laminated and pressure-bonded so that the thick film electrode surface is buried, and then fired to form a laminated ceramic structure portion. The base portion may be made of the same material as that of the first insulator layer, but in order to reduce the material cost and the capacitance of the electrode, an alumina-based material or a glass frit mixed with it at a low cost and with a low dielectric constant is used. A body ceramic is preferable. The EL element performs light emission display in a portion defined by the first electrode and the second electrode, and the electrode has both a current supply function and a pixel display function, which is suitable for various display devices. According to this, it is formed in an arbitrary pattern.
The pattern formation of the first electrode is easily realized by a printing method. Normally, an extremely fine electrode pattern is rarely required in a display panel of an EL element, and a screen printing method is sufficient, and it has an advantage that electrodes can be formed in a large area at low cost. When a fine pattern is required, the photolithographic technique may be used to form the fine pattern of the thick film electrode.

As described above, the EL element of the present invention is one in which the thin film light emitting layer is formed on the laminated ceramic structure in which the electrode is embedded between the first insulator layer and the substrate. By forming the insulator layer, which is an important component, from ceramic, a large capacity and high dielectric breakdown strength of the insulator layer are realized. The relative dielectric constant of the insulator thin film in the conventional thin film EL element is about 5 to 25 for general materials, and about 100 to 200 for PbTiO ₃ thin films and the like that are achieved under severe manufacturing conditions. With the ceramics obtained by firing the green sheet, it is possible to easily realize even a dielectric constant as high as 10,000 or more by selecting an appropriate high dielectric constant material. In addition, since the permittivity is so large, the ε · Eb.d. Value is several tens to 100 times that of the conventional thin film insulator layer. Therefore, even if the first insulator layer is formed to have a thickness of, for example, 30 microns, the capacitance of the first insulator layer is Y ₂ O ₃ , Si ₃ N ₄ , Ta ₂ O ₅ , and Al ₂ which are used in ordinary thin film EL elements. It is two orders of magnitude larger than the capacity of a general insulator layer such as O _{3, and} even as a thin film insulator layer, a large capacity of about 10 times can be easily realized compared with the above-mentioned PbTiO ₃ or SrTiO ₃ thin film. Further, since it can be used with a thickness of several tens of microns, an element free from dielectric breakdown is realized. Therefore, by adopting the insulator layer of high dielectric constant ceramic, an insulator layer which is stable against dielectric breakdown and has a large capacity is realized, and a high-luminance light emission characteristic can be obtained by driving at low voltage.

Such an insulating ceramic layer having a high dielectric constant can be manufactured in a large area at a low cost with good thickness uniformity by the green sheet method. The thickness is preferably several microns or more in terms of manufacturing problems and device stability. Further, although the stability is improved against a local dielectric breakdown by increasing the thickness, naturally the capacity is reduced in inverse proportion to the thickness, and the problem of crosstalk with an adjacent display pixel when used as a display element occurs. Less than 300 microns is preferred to occur. In order to clarify the advantages of the EL element of the present invention, the relative dielectric constant of this ceramic layer is preferably several hundreds or more, but the high dielectric constant ceramic layer of about 1,000 to 20,000 is made of various materials by the green sheet method. It can be manufactured with a composition. However, a high firing temperature in an oxidizing atmosphere is generally required, and it is necessary to use an expensive precious metal paste such as Pt, Au, or Pd as the first electrode. Some special BaTiO ₃ materials can be sintered in a neutral reducing atmosphere. In this case, nickel can also be used as an electrode material. However, in terms of ease of production and stability of properties, it is most preferable to use a low-dielectric-type high-dielectric material typified by a Pb-containing composite perovskite, and a low-cost Ag or Ag-Pd alloy with a high Ag content is used. Can be adopted.

The EL layer of the present invention is formed by forming a light emitting layer and the like on the laminated ceramic structure described above by a thin film process such as vapor deposition and sputtering.
The device is obtained. In order to improve the surface condition, the surface of the laminated ceramic may be polished before forming the light emitting layer. However, even if the light emitting layer is directly formed without polishing, no particular inconvenience occurs.

(Example) A binder was mixed with a powder composed of alumina and lead borosilicate glass to prepare a slurry, which was then cast to form a film.
A green sheet was prepared as a 0.7 mm ceramic substrate. By screen printing on this ceramic green sheet
85 atomic percent Ag and 15 atomic percent Pd
The Ag-Pd paste was formed into a striped pattern with a width of 0.33 mm and a pitch of 0.55 mm. Pb (Fe _2/3 W _1/3 ) _0.3 (Fe _1/2 Nb as a Pb-based composite perovskite material for low temperature firing
_1/2 ) _0.7 O ₃ pre-calcined powder was mixed with a binder and casting was performed to form a 40 μm thick green sheet for the first insulator layer. This green sheet was laminated and pressure-bonded onto the green sheet for a substrate on which the above-mentioned electrode pattern was printed, the unnecessary portions at the ends were cut, and then fired at 950 ° C. to form a laminated ceramic structure. About 10 by this firing
There was no shrinkage, but there was no warpage. Then ZnS
ZnS: Mn was vacuum-deposited to a thickness of 0.3 micron by the co-evaporation method of Mn and Mn. To improve the properties, heat treatment was performed in Ar for 2 hours at 650 ℃. Then, a TaAIO insulator layer having a thickness of 0.3 μm was formed as a second insulator layer by a sputtering method using a target made of a mixture of Ta ₂ O ₅ and Al ₂ O ₃ . Next, an ITO film of 0.4 micron was formed by sputtering, and
-Pd thick film stripe electrode orthogonal to 0.3 mm width, 0.5
Etching was performed at a mm pitch to form a transparent stripe electrode.
Since the ITO film was as thick as 0.4 μm, the sheet resistance was about 5 ohms and could be lowered.

In the EL device thus produced, the capacitance of the ceramic first insulator layer is very large, so there is almost no voltage drop in this layer, and the crystallinity and Mn distribution of the light emitting layer are improved by high temperature heat treatment. Moreover, in addition to the low electrode resistance, the light emission starting voltage due to the application of the AC pulse voltage was as low as 55 V, and the light emission luminance was good at about 500 cd / m ² at 80 V, 500 Hz. In the case of the one-sided insulation structure in which the thin second insulating layer was excluded, the current value was large and the light emission efficiency was poor, but the light emission starting voltage was as low as about 40 V, and the light emission luminance was about the same. The device of this example showed no dielectric breakdown even when a voltage of up to 200 V was applied, and showed high stability.

The good light emission characteristics and stability as described above are the same when ZnS: TbF ₃ of edge color light emission and ZnS: SmF _{3 of} red light emission are used as the light emitting layer in addition to ZnS: Mn. Was shown to be effective.

(Effects of the Invention) As described above, the EL device of the present invention has high stability, low voltage drive, high brightness light emission, high contrast, and low electrode resistance, so that segment display to large display capacity dot matrix display are possible. It is possible. In addition, there is almost no breakdown of the element due to dielectric breakdown and the yield is improved. Also, the adoption of laminated ceramics and the thick film process realize cost reduction compared to conventional high-priced glass substrates and heavy use of thin film processes. Is. Further, by lowering the driving voltage, the cost of the driving circuit section can be greatly reduced, and the industrial value of the present invention is great.

[Brief description of drawings]

FIG. 1 schematically shows a cross section of an EL device of the present invention. FIG. 2 shows a cross-sectional structure of a conventional thin film EL element. 11 ... Ceramic substrate, 12 ... Thick film first electrode, 13 ... High dielectric constant ceramic first insulator layer, 14, 24 ... Thin film light emitting layer, 15, 25 ...
Thin film second insulator layer, 16 ... Transparent second electrode, 21 ... Glass substrate, 22 ... Transparent electrode, 23 ... Thin film first insulator layer, 26 ... Back electrode

Claims (3)

[Claims] 1. A structure in which an electrically insulating substrate, a first electrode formed in a predetermined pattern, a first insulating layer, an electroluminescent light emitting layer and a second electrode are sequentially laminated, or In an EL device having a structure in which a second insulating layer is interposed between a light emitting layer of the structure and a second electrode, the substrate is ceramic, and the first insulating layer is a powder raw material. It is a high dielectric constant ceramic obtained by binding,
An EL device, wherein the light emitting layer and the second insulator layer are thin films, and the second electrode is a transparent electrode. 2. The EL device according to claim 1, wherein the first insulator layer is a ceramic composed of a composite perovskite containing Pb. 3. A step of forming a first green sheet by casting after mixing a binder with a powder raw material mainly composed of an oxide to form a slurry, and mixing the binder with a high dielectric constant oxide powder as a main raw material to prepare a slurry. After that, a step of forming a second green sheet by casting, a step of printing electrodes on the first green sheet, the second green sheet, or both green sheets, and laminating the first green sheet and the second green sheet A step of creating a laminated ceramic structure by pressure bonding and firing,
A method for manufacturing an EL element, comprising: a step of forming an EL light emitting layer thin film of ZnS: Mn, ZnS: TbF ₃ or the like on the laminated ceramic structure, and a step of forming a transparent conductive thin film to be a transparent electrode.