JP3914067B2 - EL display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an EL display having at least a structure in which an electrically insulating substrate, an electrode layer having a pattern on the substrate, and a dielectric layer, a light emitting layer, and a transparent electrode layer are laminated on the electrode layer.
[0002]
[Prior art]
EL elements have been put into practical use as backlights for liquid crystal displays (LCDs) and watches.
[0003]
An EL element is an element using a phenomenon in which a substance emits light when an electric field is applied, that is, an electroluminescence (EL) phenomenon.
[0004]
The EL element includes a dispersed EL element having a structure in which a powder luminescent material is dispersed in an organic substance or a hollow and electrode layers are provided on the upper and lower sides, two electrode layers and two thin film insulators on an electrically insulating substrate. There is a thin film EL element using a thin film light emitter formed in a sandwiched manner. Further, there are a DC voltage driving type and an AC voltage driving type for each driving method. Dispersion EL elements have been known for a long time and have the advantage of being easy to manufacture, but their use has been limited because of their low brightness and short lifetime. On the other hand, thin film EL elements have been widely used in recent years because of their high brightness and long life.
[0005]
FIG. 8 shows the structure of a typical double-insulated thin film EL element as a conventional thin film EL element. This thin-film EL element is a transparent electrode having a predetermined stripe pattern made of ITO having a film thickness of about 0.2 μm to 1 μm on a transparent substrate (11) such as blue plate glass used for liquid crystal displays and PDPs. A layer (12), a thin film transparent first insulator layer (13), a light emitting layer (14) having a thickness of about 0.2 μm to 1 μm, and a thin film transparent second insulator layer (15) are laminated, and further a transparent electrode The electrode layer (16) such as an Al thin film patterned in a stripe shape so as to be orthogonal to the layer (12) is formed, and the specific selected by the matrix composed of the transparent electrode layer (12) and the electrode layer (16) By selectively applying a voltage to the light emitter, the light emitter of the specific pixel emits light, and the emitted light is taken out from the substrate side. Such a thin-film insulator layer has a function of limiting the current flowing in the light-emitting layer, can suppress the dielectric breakdown of the thin-film EL element, and contributes to obtaining stable light-emitting characteristics. EL devices are widely used commercially.
[0006]
The thin film transparent insulator layers (13) and (15) are Y ₂ O _Three , Ta ₂ O _Five , Ai _Three N _Four , BaTiO _Three , Etc. are formed in a thickness of about 0.1 to 1 μm by sputtering or vapor deposition.
[0007]
As a light emitting material, ZnS added with Mn which emits yellow-orange light has been mainly used from the viewpoint of easiness of film formation and light emission characteristics. In order to produce a color display, it is indispensable to use a luminescent material that emits light in three primary colors of red, green, and blue. These materials include SrS added with blue light emitting Ce and ZnS added with Tm, ZnS added with red light emitting Sm and CaS added with Eu, ZnS added with green light emitting Tb, and CaS added with Ce. It has been known.
[0008]
In addition, the monthly display '98 April issue “Recent display technology trends”, Tanaka, p1-10, ZnS, Mn / CdSSe, etc. as materials for obtaining green light emission, ZnS: As materials for obtaining blue light emission, such as TbOF and ZnS: Tb, SrS: Cr, (SrS: Ce / ZnS) n, Ca ₂ Ga ₂ S _Four : Ce, Sr ₂ Ga ₂ S _Four A light emitting material such as Ce is disclosed. In addition, light-emitting materials such as SrS: Ce / ZnS: Mn are disclosed as materials that obtain white light emission.
[0009]
Further, among the above materials, SrS: Ce is disclosed in IDW (International Display Workshop) '97 X.Wu "Multicolor Thin-Film Ceramic Hybrid EL Displays" p593 to 596, which is used for a thin film EL element having a blue light emitting layer. ing. Further, in this document, when a light emitting layer of SrS: Ce is formed, H ₂ It is disclosed that a high-purity light-emitting layer can be obtained when formed by an electron beam evaporation method in an S atmosphere.
[0010]
However, when such an EL element is considered as a display, there still remain display quality problems such as light oozing out to the outer periphery of the pixel and light emission distribution at the end of the pixel.
[0011]
In order to solve the display problem in such a thin film EL element, Japanese Patent Application Laid-Open No. 60-257097 discloses a method of separating a plurality of phosphors and forming a light absorber layer between pixels, Japanese Patent Application Laid-Open No. 11-265790. Japanese Patent Application Laid-Open No. 2003-259259 discloses a method of forming a light absorption layer around a light emitting layer.
[0012]
However, although these methods are effective for bleeding out light between pixels, there is a problem in that uneven light emission at the pixel end in the low luminance region occurs.
[0013]
That is, in the conventional EL element, there is a problem that a light distribution between pixels and a luminance distribution are generated at both ends on the transparent electrode side due to an end effect. FIG. 9 shows a light emission state of a pixel of a typical EL element. From this figure, it can be seen that the pixel end emits light with high luminance. These results indicate that the light emission at the pixel end portion starts early in the low voltage region, and the light emission distribution in the low luminance region was also observed in the actual element. This has led to a decrease in the uniformity of light emission within the pixel, which in turn has been a factor in reducing the display quality.
[0014]
[Problems to be solved by the invention]
An object of the present invention is to prevent a luminance distribution from occurring at both ends of a light emitting pixel due to an end effect, and to realize a high-quality EL element having light emission uniformity within the pixel.
[0015]
[Means for Solving the Problems]
That is, the above object is achieved by the following method of the present invention.
(1) It has a substrate having electrical insulation, a first electrode and a second electrode patterned so as to form a matrix circuit on the substrate, and at least a dielectric is provided between these electrodes. An EL device having a layer and an inorganic thin-film light emitting layer, Of the first and second electrodes Closer to the light emitting layer Top The electrode is a transparent electrode, and the light emitting layer is separated into a similar pattern in parallel with the transparent electrode, and the transparent electrode is formed to overcoat the light emitting layer. The width of each of the transparent electrodes patterned in the direction perpendicular to the longitudinal direction of the light emitting layer pattern along the extending direction of the lower electrode paired with the upper electrode of the first and second electrodes Is wider than the width of the corresponding light emitting layer EL display.
(2) The transparent electrode is In the direction perpendicular to the light emitting layer pattern longitudinal direction along the extending direction of the lower electrode, From the end of the transparent electrode The distance to the edge of the light emitting layer is Range from 0.5 μm to 5.0 μm on one side It is formed to be (1) EL display.
(3) The transparent electrode is at least It is formed so as to cover the upper surface of the light emitting layer and the side surface of the light emitting layer located in the direction orthogonal to the longitudinal direction of the light emitting layer pattern along the extending direction of the lower electrode. The EL display according to (1) or (2) above.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
The EL display of the present invention has a substrate having electrical insulation, and first and second electrodes patterned so as to form a matrix circuit on the substrate, and between these electrodes, An EL device having at least a dielectric layer and an inorganic thin-film light-emitting layer, wherein one of the electrodes closer to the light-emitting layer is a transparent electrode, and the light-emitting layer is separated into the same pattern in parallel with the transparent electrode The transparent electrode is formed so as to overcoat the light emitting layer.
[0017]
In this way, by patterning the light emitting layer in the same pattern as the transparent electrode and forming the transparent electrode so as to overcoat the light emitting layer, it is possible to suppress an increase in luminance particularly at the pixel end during low luminance emission, The light emission in the pixel can be made uniform.
[0018]
FIG. 1 is a schematic cross-sectional view showing a configuration example of an EL display according to the present invention. The EL device of the present invention has a lower electrode layer (first electrode layer) 2 having a predetermined pattern on a substrate 1 having electrical insulation, and a first dielectric layer 3 which is a thick film dielectric thereon, Further, a second dielectric layer 4, a thin film insulator layer 5, a light emitting layer 6, a thin film insulator layer 7, and a transparent electrode layer (second electrode layer) 9 are laminated on the first dielectric layer 3. is there. The thin film insulator layers 5 and 7 may be omitted.
[0019]
The lower electrode layer 2 and the upper transparent electrode layer 9 are each formed in a stripe shape and are arranged in directions orthogonal to each other to form a matrix. By selecting each of the lower electrode layer and the upper transparent electrode layer and selectively applying a voltage to the light emitting layer at the orthogonal portion of both electrodes, it is possible to obtain light emission of a specific pixel.
[0020]
In addition, since the overcoat amount d of the transparent electrode is difficult to configure an actual device in terms of pattern accuracy, it is desirable that the transparent electrode has an overcoat amount of 0.5 μm or more on one side from the end of the light emitting layer. On the other hand, it is desirable that the upper limit be 5.0 μm or less because the power consumption during device operation increases, the light emitting region becomes smaller, and the probability of occurrence of a short circuit with an adjacent pixel increases.
[0021]
FIG. 10 shows that the luminance at the center of the pixel is 150 cd / m. ² 900cd / m ² The luminance ratio 20 μm inside from the center of the pixel and the end of the pixel (light emitting layer pattern) is shown. As is apparent from the figure, when the overcoat amount exceeds 2.0 μm, it is difficult to sufficiently obtain the light emission luminance at the edge at low luminance. On the other hand, when the thickness is 5.0 μm or more, the light emission luminance at the pixel end cannot be sufficiently obtained even at high luminance. Accordingly, the overcoat amount d is preferably 0.5 to 2.5 μm, more preferably 1.0 to 2.0 μm.
[0022]
The transparent electrode layer is made of ITO or SnO having a thickness of 0.2 μm to 1 μm. ₂ (Nesa film), oxide conductive materials such as ZnO-Al, and the like are used. As a method for forming the transparent electrode layer, a known technique such as vapor deposition as well as sputtering may be used.
[0023]
The patterning of the transparent electrode can be performed by a known patterning method. For example, after forming the transparent electrode, the photoresist may be formed larger than the pixel width and removed by etching.
[0024]
The transparent electrode is usually formed so as to have a plurality of stripe patterns, the line width is one pixel width, and the space between the lines becomes a non-light emitting region. Therefore, the space between the lines can be made as small as possible. preferable. Although it depends on the resolution of the target display, for example, the line width is preferably 100 to 1000 μm, and the space g is about 10 to 40 μm, more preferably about 15 to 25 μm.
[0025]
For example, in the case of a 10.4 inch diagonal display with VGA (640 × 480) resolution, if it is a single light emitting layer, a line width of 290 to 320 μm and a space of 10 to 40 μm are required depending on the aperture ratio. is there.
[0026]
The overcoat is an extending direction (pattern direction) of at least a rectangular pixel and another electrode that is paired with the transparent electrode. In other words, it may be overcoated so as to project in the direction perpendicular to the longitudinal direction of the transparent electrode or light emitting layer pattern, that is, in the gap direction. Note that the overcoat portion is preferably formed so as to cover the light emitting layer, the dielectric layer, that is, the end portion of the pixel portion. That is, it is preferable that the transparent electrode covers not only the upper surface so as to form an overhang from the pixel formation region, but also covers the side surface portion of the pixel.
[0027]
The substrate is not particularly limited as long as it has electrical insulation and can maintain a predetermined heat resistance without contaminating the lower electrode layer and the dielectric layer formed thereon.
[0028]
Specific materials include alumina (Al ₂ O _Three ), Quartz glass (SiO ₂ ), Magnesia (MgO), forsterite (2MgO · SiO) ₂ ), Steatite (MgO.SiO) ₂ ), Mullite (3Al ₂ O _Three ・ 2SiO ₂ ), Beryllia (BeO), zirconia (ZrO) ₂ ), Aluminum nitride (AlN), silicon nitride (SiN), ceramic substrate such as silicon carbide (SiC), crystallized glass, high heat-resistant glass, etc., and metal substrates that have been subjected to a brazing treatment are also used. Is possible.
[0029]
Of these, crystallized glass, high heat-resistant glass, and blue plate glass, if matched with the firing temperature of the dielectric layer to be formed, are low cost, surface property, flatness, and easy to produce a large area substrate. Therefore, it is preferable.
[0030]
The lower electrode layer is formed to have a plurality of stripe patterns, the line width is one pixel width, and the space between the lines becomes a non-light emitting region. Therefore, the space between the lines can be made as small as possible. Preferably, depending on the target display resolution, for example, a line width of 200 to 500 μm and a space of about 20 μm are required.
[0031]
A material for the lower electrode layer is preferably a material that has high conductivity, is not damaged when the dielectric layer is formed, and has low reactivity with the dielectric layer and the light emitting layer. Such lower electrode layer materials include noble metals such as Au, Pt, Pd, Ir, and Ag, noble metal alloys such as Au—Pd, Au—Pt, Ag—Pd, and Ag—Pt, and Ag—Pd—Cu. An electrode material having a precious metal such as a main component and a base metal element added is preferable because oxidation resistance to an oxidizing atmosphere during firing of the dielectric layer can be easily obtained. ITO and SnO ₂ (Nesa film), oxide conductive materials such as ZnO-Al may be used, and further, base metals such as Ni and Cu are used, and these non-metals oxidize the partial pressure of oxygen when firing the dielectric layer. It can also be set and used in a range that is not. As a method for forming the lower electrode layer, a known technique such as sputtering, vapor deposition, or plating may be used.
[0032]
The thick film dielectric layer needs to have a high dielectric constant and a high withstand voltage, and is required to be a material that can be fired at a low temperature in consideration of the heat resistance of the substrate.
[0033]
Here, the thick film dielectric layer is a ceramic layer formed by firing a powdery insulator material by a so-called thick film method. The thick film dielectric layer is formed, for example, by printing and baking an insulator paste prepared by mixing a binder and a solvent with a powdery insulator material on a substrate on which a lower electrode layer is formed. be able to. Alternatively, a green sheet may be formed by casting an insulating paste to form a laminate.
[0034]
The conditions for the binder removal treatment performed before firing may be normal.
[0035]
The atmosphere during firing may be appropriately determined according to the type of the conductive material in the electrode layer paste, but when firing in an oxidizing atmosphere, ordinary firing in the air may be performed.
[0036]
The holding temperature during firing may be appropriately determined according to the type of the insulator layer, but is usually about 700 to 1200 ° C., preferably 1000 ° C. or less. The temperature holding time during firing is preferably 0.05 to 5 hours, particularly preferably 0.1 to 3 hours.
[0037]
Moreover, you may anneal-treat as needed.
[0038]
Here, when the relative dielectric constants of the thick dielectric layer and the light emitting layer are e1 and e2, the film thicknesses are d1 and d2, and the voltage Vo is applied between the upper electrode layer and the lower electrode layer, the dielectric layer is applied to the light emitting layer. The voltage V2 is expressed by the following equation.
[0039]
V2 / Vo = (e1 * d2) / (e1 * d2 + e2 * d1) ------ (1)
Assuming that the relative dielectric constant of the light emitting layer is e2 = 10 and the film thickness is d2 = 1 μm,
V2 / Vo = e1 / (e1 + 10 × d1) ------- (2)
[0040]
Since the voltage effectively applied to the light emitting layer is at least 50% or more of the applied voltage, preferably 80% or more, more preferably 90% or more,
[0041]
In the case of 50% or more, e1 ≧ 10 × d1 -------- (3)
In the case of 80% or more, e1 ≧ 40 × d1 -------- (4)
In the case of 90% or more, e1 ≧ 90 × d1 -------- (5)
[0042]
That is, the relative dielectric constant of the dielectric layer needs to be at least 10 times, preferably 40 times or more, more preferably 90 times or more of the film thickness when the unit is expressed in μm.
[0043]
The film thickness of the thick film dielectric is required to be thick in order to eliminate pinholes formed by electrode steps or dust in the manufacturing process, and is at least 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more. Necessary. The upper limit is not particularly limited, but is usually about 50 μm.
[0044]
For example, when the thickness of the dielectric layer is 20 μm, the relative dielectric constant needs to be 200 to 800 to 1800 or more, and when the thickness of the dielectric layer is 30 μm, the relative dielectric constant is 300 to 1200. 2700 is required.
[0045]
Various materials can be considered as such a high dielectric constant thick film material, but considering the heat resistance limitation of the substrate material, a high dielectric constant ceramic composition that can be formed at a low temperature is desirable.
[0046]
For example, BaTiO _Three , (Ba _x Ca _1-x ) TiO _Three , (Ba _x Sr _1-x ) TiO _Three , PbTiO _Three , Pb (Zr _x Ti _1-x ) _Three Dielectrics having a perovskite structure, such as ferroelectric materials, Pb (Mg _1/3 Ni _2/3 ) O _Three Composite perovskite relaxor type ferroelectric materials represented by _Four Ti _Three O ₁₂ , SrBi ₂ Ta ₂ O ₉ Bismuth layered compound represented by (Sr _x Ba _1-x Nb ₂ O ₆ , PbNb ₂ O ₆ Tungsten bronze type ferroelectric materials such as the above are preferred because of their high dielectric constant and easy firing.
[0047]
In addition, the dielectric material containing lead in its composition has a low melting point of lead oxide as low as 888 ° C., and lead oxide and other oxide materials such as SiO 2 ₂ And CuO, Bi ₂ O _Three , Fe ₂ O _Three Since a liquid phase is formed at a low temperature of about 700 ° C. to 800 ° C., etc., firing is easy at a low temperature and a high dielectric constant is easily obtained, which is preferable. For example, Pb (Zr _x Ti _1-x ) _Three Perovskite structure dielectric materials such as Pb (Mg _1/3 Ni _2/3 ) O _Three Composite perovskite relaxor type ferroelectric materials represented by PbNbO ₆ Examples thereof include tungsten bronze type ferroelectric materials. These can easily form a dielectric having a relative dielectric constant of 1000 to 10,000 at a firing temperature of 800 to 900 ° C., which is the upper limit heat resistance temperature of a normal ceramic substrate such as alumina ceramics.
[0048]
Since the purpose of the high dielectric constant dielectric layer laminated on the thick film dielectric layer is to improve the surface flatness of the thick film dielectric layer, it is necessary to use a solution coating firing method.
[0049]
The solution coating and firing method refers to a method in which a dielectric material precursor solution such as a sol-gel method or a MOD method is applied to a substrate and a dielectric layer is formed by firing.
[0050]
In the sol-gel method, generally, a predetermined amount of water is added to a metal alkoxide dissolved in a solvent, and a precursor solution of a sol having an MOM bond formed by hydrolysis and polycondensation reaction is applied to a substrate and baked. This is a method for forming a film. The MOD (Metal-Organic Decomposition) method forms a film by dissolving a metal salt of a carboxylic acid having an MO bond in an organic solvent to form a precursor solution, and applying and baking the substrate. Is the method. Here, the precursor solution refers to a solution containing an intermediate compound produced by dissolving a raw material compound in a solvent in a film forming method such as a sol-gel method or a MOD method.
[0051]
The sol-gel method and the MOD method are not completely separate methods and are generally used in combination with each other. For example, when forming a PZT film, it is common to use lead acetate as the Pb source and adjust the solution using the alkoxide as the Ti and Zr sources. In addition, the two methods of the sol-gel method and the MOD method may be collectively referred to as the sol-gel method, but in any case, a film is formed by applying a precursor solution to a substrate and baking it. Then, it is set as the solution application baking method. Moreover, even if the solution is a mixture of submicron-sized dielectric particles and a dielectric precursor solution, it is included in the dielectric precursor solution of the present invention, and the solution is applied to a substrate and fired. It is included in the solution coating firing method of the present invention.
[0052]
In the solution coating and firing method, in both the sol-gel method and the MOD method, the elements constituting the dielectric are uniformly mixed in the order of sub-μm or less. Compared with the method using powder sintering, it is characterized in that a dense dielectric can be synthesized at an extremely low temperature.
[0053]
The main purpose of using the solution coating and baking method is that the dielectric layer formed by this method is formed through the step of applying and baking the precursor solution. Since a thin layer is formed on the surface, the step on the substrate surface is flattened, and the surface flatness of the thick ceramic dielectric layer of the EL element is remarkably improved, and the thin film light emission formed thereon The layer uniformity can be greatly improved.
[0054]
Therefore, the thickness of the dielectric layer formed by the solution coating and firing method is desired to be 0.5 μm or more, preferably 1 μm or more, more preferably 2 μm or more in order to sufficiently flatten the unevenness of the thick film surface.
[0055]
Here, the influence on the relative dielectric constant of the entire dielectric layer due to the lamination of the dielectric layers by this solution coating and firing method will be described. When the relative dielectric constants of the thick dielectric layer and the high dielectric constant dielectric layer formed by the solution coating firing method are e3 and e4, respectively, and the total film thickness of each layer is d3 and d4, the laminated dielectric The effective relative dielectric constant e5 of the entire layer is expressed by the following equation. (Here, the film thickness of the entire laminated dielectric layer is converted into a dielectric constant assuming that it does not change as d3)
[0056]
e5 = e3 × 1 / [1+ (e3 / e4) × (d4 / d3)] ------- (6)
If this equation is transformed,
e4 / d4 = e3 * e5 / (d3 * (e3-e5)) ------- (7)
[0057]
Based on the above discussion, the effective relative dielectric constant of the entire laminated dielectric layer formed by the solution coating and baking method is preferable when the thickness of the thick film layer is 30 μm. Is 1200 to 2700 or more. Therefore, for example, when a thick film having a relative dielectric constant of 4000 is used to obtain an effective dielectric constant of 2700, the ratio of the relative dielectric constant to the film thickness of the dielectric layer formed by the solution coating and baking method needs to be 277 or more. If the dielectric constant of the thick dielectric layer is 3000, the ratio is 900.
[0058]
As described above, the film thickness of the dielectric layer formed by the solution coating firing method is at least 0.5 μm or more, preferably 1 μm or more, more preferably 2 μm or more. For this reason, the relative dielectric constant is desirably as high as possible, and is at least 250 or more, preferably 500 or more.
[0059]
As described above, the high dielectric constant layer formed by the solution coating firing method needs to have a large film thickness and a high dielectric constant. Examples of such a high dielectric constant material include BaTiO. _Three , (Ba _x Ca _1-x ) TiO _Three , (Ba _x Sr _1-x ) TiO _Three , PbTiO _Three , Pb (Zr _x Ti _1-x ) _Three Dielectrics having a perovskite structure, such as ferroelectric materials, Pb (Mg _1/3 Ni _2/3 ) O _Three Composite perovskite relaxor type ferroelectric materials represented by _Four Ti _Three O ₁₂ , SrBi ₂ Ta ₂ O ₉ Bismuth Bismuth Layered Compound (Sr _x Ba _1-x Nb ₂ O ₆ , PbNbO ₆ Examples thereof include tungsten bronze type ferroelectric materials. Among these, BaTiO _Three A ferroelectric material having a perovskite structure such as PZT is preferable because it has a high dielectric constant and can be easily formed at a relatively low temperature.
[0060]
Although it does not specifically limit as a material of a light emitting layer, Well-known materials, such as ZnS which doped Mn mentioned above, can be used. Among these, SrS: Ce and a barium thioaluminate phosphor layer which is a blue light emitter are particularly preferable because excellent characteristics can be obtained. The thickness of the light emitting layer is not particularly limited, but if it is too thick, the driving voltage increases, and if it is too thin, the light emission efficiency decreases. Specifically, although it depends on the light emitting material, it is preferably about 100 to 2000 nm.
[0061]
As a method for forming the light emitting layer, a vapor deposition method can be used. As the vapor deposition method, a physical vapor deposition method such as sputtering or vapor deposition or a chemical vapor deposition method such as CVD is preferable. Further, as described above, particularly when a light emitting layer of SrS: Ce is formed, H ₂ When the substrate temperature during film formation is maintained at 500 ° C. to 600 ° C. by an electron beam evaporation method in an S atmosphere, a high-purity light emitting layer can be obtained.
[0062]
After the light emitting layer is formed, heat treatment is preferably performed. Heat treatment may be performed after laminating the electrode layer, dielectric layer, and light emitting layer from the substrate side, or the electrode layer, dielectric layer, light emitting layer, insulator layer, or electrode layer is formed on the substrate side from the substrate side. Then, heat treatment (cap annealing) may be performed. The temperature of the heat treatment depends on the light emitting layer to be formed, but in the case of SrS: Ce, it is preferably 500 ° C. to 600 ° C. or higher, lower than the firing temperature of the dielectric layer, and the processing time is 10 to 600 minutes. The atmosphere during the heat treatment is preferably in Ar.
[0063]
After the formation of the light emitting layer, an upper thin film insulating layer and a transparent electrode are sequentially laminated. At this time, the light emitting layer is separated into a width of one pixel orthogonal to the first electrode, and the transparent electrode is formed to have a width wider than that of the light emitting layer and overcoated. The upper thin film insulating layer may be separated in the same manner as the light emitting layer, or may be formed on the entire surface of the element as shown in FIG. In FIG. 2, the same components as those in FIG. Also in this case, the amount of overcoat is preferably an amount defined by the distance from the end of the light emitting layer as described above.
[0064]
Separation of the light emitting layer and, if necessary, the insulating layer can be performed using a known patterning technique. For example, the photoresist may be patterned in the pixel region and then removed by etching and separated.
[0065]
The upper / lower thin film insulator layer may be omitted as described above, but the upper thin film insulator layer preferably has this.
[0066]
This thin-film insulator layer functions as a function of adjusting the electronic state of the interface between the light emitting layer and the dielectric layer to stabilize and improve electron injection into the light emitting layer, and this electronic state is The main purpose is to improve the positive / negative target of the light emission characteristics during AC drive by configuring both sides, and it is not necessary to consider the function of maintaining the dielectric strength, which is the role of the dielectric layer The film thickness may be small.
[0067]
This thin-film insulator layer has a resistivity of 10 ⁸ Ω · cm or more, especially 10 ^Ten -10 ¹⁸ About Ω · cm is preferable. Further, it is preferably a substance having a relatively high relative dielectric constant, and the relative dielectric constant ε is preferably ε = 3 or more. As a constituent material of the thin film insulator layer, for example, silicon oxide (SiO 2 ₂ ), Silicon nitride (SiN), tantalum oxide (Ta ₂ O _Five ), Yttrium oxide (Y ₂ O _Three ), Zirconia (ZrO ₂ ), Silicon oxynitride (SiON), alumina (Al ₂ O _Three ), Etc. can be used. As a method for forming the thin film insulator layer, a sputtering method, a vapor deposition method, or a CVD method can be used. The film thickness of the thin film insulator layer is preferably about 10 to 1000 nm, particularly preferably about 20 to 200 nm.
[0068]
Although the above-described EL element has only a single light emitting layer, the EL element of the present invention is not limited to such a configuration, and a plurality of light emitting layers may be stacked in the film thickness direction, A configuration may be adopted in which different types of light emitting layers (pixels) are combined and arranged in a matrix.
[0069]
In the above-described EL element, the configuration in which the light from the light emitting layer is extracted from the upper ITO electrode side has been described. However, the EL element of the present invention is not limited to such a configuration, and emits light from the insulating substrate side. The light of the layer may be extracted. In this case, a transparent substrate such as heat resistant glass may be used as the insulating substrate, and a transparent electrode such as ITO may be used as the lower electrode.
[0070]
【Example】
Examples of the present invention are specifically shown below and described in more detail.
[0071]
[Example 1]
A 99.6% pure alumina substrate was surface-polished, and an Au thin film to which a trace amount of additive was added was formed on the substrate by sputtering to a thickness of 1 μm, and stabilized by heat treatment at 700 ° C. This Au thin film was patterned into a large number of stripes having a width of 300 μm and a space of 30 μm by using a photoetching method.
[0072]
A 10 μm PZT dielectric layer, which is a lead-based dielectric layer, was formed on this substrate by using a screen printing method as a first dielectric layer. After printing, baking was performed at 800 ° C.
[0073]
As the planarization layer of the first dielectric layer, the operation of applying the PZT precursor solution to the substrate by spin coating using the sol-gel solution and baking at 700 ° C. for 15 minutes was repeated twice. .
[0074]
On the above substrate, Al as a thin film insulating layer ₂ O _Three Film, 50 nm and ZnS: Mn, 200 nm as light emitting layer by electron beam evaporation method ₂ In the S atmosphere, the substrate temperature during film formation was maintained at 150 ° C. Furthermore, Al as the upper insulator layer ₂ O _Three A film, 50 nm, was formed.
[0075]
A negative resist was formed on the substrate by a 3.0 μm spin coating method, and a pattern was formed in a stripe shape having a width of 300 μm and a space of 30 μm in a form perpendicular to the Au electrode using a normal photolithography process. At this time, the resist was patterned so that 300 μm remained on the light emitting layer.
[0076]
The substrate was immersed in a mixed solution of an inorganic acid and an organic solvent, and unnecessary portions between pixels were removed by etching. Further, after the etching was completed, the resist was removed using an organic solvent.
[0077]
Next, an ITO thin film having a thickness of 0.5 μm was formed as a transparent electrode by sputtering.
[0078]
A negative resist was formed on the substrate by a 3.0 [mu] m spin coating method, and a pattern was formed in a stripe shape with a width of 303 [mu] m and a space of 27 [mu] m in a form perpendicular to the Au electrode using a normal photolithography process. At this time, the resist was patterned to leave a space between the pixels.
[0079]
The negative resist used as a mask was removed using an organic solvent, and the ITO electrode was separated into a width of 303 μm and a space of 27 μm. That is, the overcoat amount was 1.5 μm on one side.
[0080]
Furthermore, an Al thin film was formed as a lead electrode by a sputtering method to obtain an EL element.
[0081]
The shape of the pixel actually obtained was formed in such a way that the ITO electrode spreads on the phosphor by 1.5 μm on one side.
[0082]
The light emission characteristic was measured by applying a voltage between the lower electrode and the upper transparent electrode of the obtained element structure with a pulse width of 150 Hz and 50 μsec.
[0083]
FIG. 3 shows the measurement result of the light emission intensity distribution between the pixels of the structure shown in FIG. 1 in which the light emitting layer is separated and ITO is overcoated. From the state of light emission between the pixels shown in this figure, uniform light emission characteristics were obtained in the pixels from low to high luminance, and a luminance difference of about 4: 1 was obtained as the luminance difference between the pixels.
[0084]
Further, as a comparative sample 1, an element having a conventional structure as shown in FIG. 4 in which only the ITO electrode of the upper transparent electrode was separated without separating the light emitting layer was also produced. An alternating pulse voltage was applied to the element having this structure to emit light. FIG. 5 shows the emission intensity spectrum between pixels measured using a microspot luminance meter. The brightness at the center of the pixel is 100cd / m ² Then, it can be seen that the light oozes out between the ITO electrodes and emits light with a luminance about twice as high as that of the center portion of the pixel.
[0085]
250cd / m ² The luminance difference between the pixel end portion and the central portion increases by about 1.5 times, and the applied voltage is increased and the luminance difference in the pixel is reduced. 900cd / m ² When light was emitted up to, the light emission in the pixel became almost uniform. At this time, the luminance difference between the pixels and within the pixels was about 2: 1.
[0086]
Further, as Comparative Sample 2, an element having the structure shown in FIG. A 150 Hz AC pulse voltage was applied to the element having this structure to emit light. FIG. 7 shows the emission intensity spectrum between pixels measured using a micro luminance meter. When the light emitting state becomes high luminance, there is no light emitting layer between pixels, so 400 cd / m ² Thus, the luminance difference between the pixels and within the pixels was about 3: 1. When the light emitting layer is separated, an effect is seen in separating the light emission between the pixels, but the pixel end portion at the low luminance is higher in luminance than the central portion of the pixel as in the structure of FIG.
[0087]
This result shows that the effect is insufficient only by separating the light emitting layer and the transparent electrode with the same width.
[0088]
From these results, the structure in which the transparent electrode is overcoated on the light emitting layer has the effect that the pixels of the EL element emit light uniformly from the low luminance from the state where the low voltage is applied, and the bleeding between the transparent electrodes is suppressed. It is clear.
[0089]
[Example 2]
In Example 1, as shown in FIG. 2, after forming the light emitting layer, patterning is performed before forming the upper insulator layer, and the ITO transparent electrode is formed as it is without separating the upper insulator layer. did. The other elements were obtained in the same manner as in Example 1.
[0090]
When the obtained device was evaluated in the same manner as in Example 1, the result was the same as in Example 1.
[0091]
【The invention's effect】
As described above, the effect of the present invention is clear. According to the present invention, it is possible to solve the distribution of light emission in a pixel, which has been a problem in conventional EL elements, and to provide an EL element having uniform light emission characteristics.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a structural example of a thin film EL element of the present invention.
FIG. 2 is a schematic cross-sectional view showing another configuration example of the thin film EL element of the present invention.
FIG. 3 is a spectrum showing a measurement result of light emission intensity between pixels of an example.
FIG. 4 is a schematic cross-sectional view showing a conventional structure in which only ITO is separated.
5 is a spectrum showing the result of measuring the emission intensity between pixels of the comparative sample in FIG. 4;
FIG. 6 is a schematic cross-sectional view showing the structure of an EL element in which a light emitting layer and a transparent electrode are separated by an equal width.
7 is a spectrum showing a measurement result of light emission intensity between pixels of the comparative sample in FIG. 6;
FIG. 8 is a schematic cross-sectional view showing the structure of a conventional EL element.
FIG. 9 is a drawing-substituting photograph showing a light emission state of a typical conventional pixel.
FIG. 10 is a graph showing a luminance ratio between the center and end of a pixel.
[Explanation of symbols]
1 Substrate
2 First electrode layer
3 Thick film dielectric layer (first dielectric layer)
4 Thin film transparent insulator (lower thin film insulator layer)
5 Light emitting layer
6 Transparent insulator layer (upper insulator layer)
7 Second electrode layer
11 Substrate
12 First electrode layer
13 Dielectric layer
13a Thick film dielectric layer (first dielectric layer)
14 Light emitting layer
15 Thin insulator layer

Claims (3)

A substrate having electrical insulation, and a first electrode and a second electrode patterned to form a matrix circuit on the substrate;
An EL element having at least a dielectric layer and an inorganic thin-film light emitting layer between these electrodes,
Of the first and second electrodes, the upper electrode closer to the light emitting layer is a transparent electrode, and the light emitting layer is separated into a similar pattern in parallel with the transparent electrode, and the transparent electrode is placed on the light emitting layer. A pattern is formed in a direction orthogonal to the longitudinal direction of the light emitting layer pattern along the extending direction of the lower electrode that is paired with the upper electrode of the first and second electrodes. An EL display in which the width of each of the formed transparent electrodes is wider than the width of the corresponding light emitting layer . The transparent electrode has a distance of 0.5 μm to 5.0 μm on one side from the end of the transparent electrode to the light emitting layer in a direction perpendicular to the light emitting layer pattern longitudinal direction along the extending direction of the lower electrode . The EL display according to claim 1, wherein the EL display is formed to be in a range. The transparent electrode is formed so as to cover at least an upper surface of the light emitting layer and a side surface of the light emitting layer located in a direction perpendicular to the longitudinal direction of the light emitting layer pattern along the extending direction of the lower electrode. claim 1 or 2 of the EL display are.

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