JP4831939B2 - Luminescent thin film and light emitting element - Google Patents

Description

  The present invention relates to a light emitter thin film and a light emitting element.

  A thin film EL element (hereinafter referred to as “inorganic EL element”) having a light emitting layer composed of an inorganic substance using an electroluminescence (EL) phenomenon has a long element life and excellent durability. It has good characteristics. Therefore, in recent years, inorganic EL elements have been actively studied as small or large light-emitting elements for flat displays.

  FIG. 5 is a perspective view showing a main part of a typical configuration of a conventional inorganic EL element. The EL element 20 is a double insulation type thin film EL element, and is formed on a transparent substrate 21 having electrical insulation, in a stripe shape, a lower electrode layer 22, a lower insulator layer 24, a light emitter layer 26, an upper insulation. The body layer 28 and the upper electrode layer 30 provided in a stripe shape are laminated in this order.

As the transparent substrate 21, a transparent substrate such as blue plate glass generally used for an LCD, a PDP (plasma display panel) or the like is employed. The lower electrode layer 22 is usually made of ITO having a thickness of about 0.1 to 1 μm. On the other hand, the upper electrode layer 30 is made of a metal such as Al. The lower insulator layer 24 and the upper insulator layer 28 are thin films having a thickness of about 0.1 to 1 μm formed by sputtering, vapor deposition, or the like, and are usually Y ₂ O ₃ , Ta ₂ O ₅ , AlN, BaTiO _3. Etc. The light emitter layer 26 is generally made of a light emitter containing a dopant serving as a light emission center, and its film thickness is usually about 0.05 to 1 μm.

  In the conventional inorganic EL element having such a configuration, one of the lower electrode layer 22 and the upper electrode layer 30 is a row electrode and the other is a column electrode, and the extending directions of both are arranged so as to be orthogonal to each other. That is, a matrix electrode is constituted by both the electrode layers 22 and 30, and the light emitting layer 26 at the intersection of the row electrode and the column electrode becomes a pixel. By selectively applying an AC voltage or a pulse voltage from the AC power supply 32 to each pixel constituted by the matrix electrodes, the luminescent layer 26 emits electroluminescence, and the emitted light is extracted from the transparent substrate 21 side.

  Among the inorganic EL elements having such a configuration, a yellow thin-colored monochrome thin film display has already been put into practical use. The phosphor layer employed in such a display is, for example, a phosphor having a base material of ZnS and an emission center of Mn as described in Non-Patent Documents 1 and 2 (hereinafter referred to as “ZnS: Mn”). It is described in the above.)

On the other hand, in order to use inorganic EL elements for display applications such as personal computers and televisions, colorization is inevitably required. For this purpose, phosphors that emit light corresponding to the three primary colors of red (R), green (G), and blue (B) are required. As phosphors capable of emitting each color, as blue light-emitting phosphors, SrS: Ce, SrGa ₂ S ₄ : Ce and ZnS: Tm, as red light-emitting phosphors, ZnS: Sm and CaS: Eu, and green light-emitting phosphors ZnS: Tb, CaS: Ce, and the like are known. However, none of these phosphors satisfy the characteristics of both emission luminance and color purity at the same time, and in order to obtain light emission of pure colors of RGB, only light emission of a specific wavelength is selected through a color filter. Needed to be removed. Therefore, the intensity (luminance) of light emission is insufficient for using such a conventional inorganic EL element for display applications, for example.

In order to eliminate such inconvenience, for example, Patent Document 1 discloses that the light emitting layer of a thin film electroluminescence (TFEL) element is made of an alkaline earth element or Zn selected from the group consisting of Ba, Ca and Sr. When it is assumed that RE is a rare earth element, it is represented by the composition formula of MAL _y S _4−x O _x : RE, and _{x in} the composition formula is 0.5 ≦ x ≦ 3 An aluminate blue light-emitting phosphor material that is a real number in the range of 0.5 and y is a real number in the range of 1.5 ≦ y ≦ 2.5 is disclosed. This phosphor material has been proposed with the intention of providing a blue-emitting electroluminescent material having high luminance and excellent color purity.
JP 2001-262140 A V. Marrello, Aare Onton, “Dependence of Electroluminescence Efficiency and Memory Effect on Mn Concentration in ZnS: Mn ACTEL Devices”, IEEE Transactions on Electron Devices, The IEEE Electron Devices Society, September 1980, Vol. ED-27, No. 9, p. 1767-1770 W Tang, DC Cameron, "Electroluminescent zinc sulphide devices produced by sol-gel processing", Thin Solid Films, Elsevier Sciences SA, 1996, Vol. 280, p. 221-226

  However, the display has recently been eagerly desired to have higher luminance, and even conventional inorganic EL elements such as those described in Patent Document 1 sufficiently satisfy the requirements. It is not a thing.

  Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a light-emitting thin film and a light-emitting element capable of further improving the light emission luminance as compared with the conventional case.

  In the process of intensive research to achieve the above-described object, the present inventors have found that the content ratio of these materials in the phosphors used in combination with specific materials is such that the luminance of conventional phosphors decreases. Adjusted to the numerical range. As a result, the inventors have found that the tendency of luminance with respect to the content ratio of these materials is different from that observed in conventional phosphors, and have completed the present invention.

  The phosphor thin film of the present invention contains an alkaline earth metal element, a group 13 metal element, a rare earth element and sulfur, and the content ratio of the rare earth element to the total amount of the alkaline earth metal element and the rare earth element is 10 It is characterized by being at least atomic percent.

  Conventionally, various studies have been made on the correlation (hereinafter referred to as “density-luminance correlation”) between the content ratio (concentration) of the luminescent center material in the phosphor thin film and the luminance. According to the results of these studies, even if the concentration of the luminescent center material in the luminescent thin film is simply increased, the luminance does not improve but tends to decrease. Moreover, it is said that the concentration of the luminescent center material having the maximum luminance is about several atomic% at the highest.

  For example, Non-Patent Document 1 examines the concentration-luminance correlation for a phosphor thin film composed of ZnS: Mn. As a result, it has been found that when the Mn concentration is 0.1 to 0.3% by mass, the luminous efficiency becomes a maximum value, and the luminous efficiency tends to decrease as the Mn concentration becomes lower or higher (for example, FIG. 1 of Non-Patent Document 1). Further, Non-Patent Document 2 examines the concentration-luminance correlation for an EL element including a light emitting layer composed of ZnS: Mn or ZnS: Tb. As a result, when the Mn concentration (Mn / Zn) and the Tb concentration (Tb / Zn) are in the vicinity of 1 atomic%, the luminance reaches the maximum value, and the luminance decreases as these concentrations are lower or higher than the vicinity of 1 atomic%. (See, for example, FIG. 7 and FIG. 14 of Non-Patent Document 2).

  In the conventional research, concentration quenching of the luminescent center material is cited as a factor in which the luminance of the luminescent thin film exhibits a maximum value at several atomic% of the concentration of the luminescent center material. When the concentration of the luminescent center material increases, the molecules of the excited luminescent center material tend to be adjacent to the molecules of the unexcited luminescent center material. For this reason, energy is exchanged between adjacent excited molecules and unexcited molecules, and the excited molecules are considered to return to the ground state without emitting light.

  Such a phenomenon of concentration quenching has been reported in various fields in the past, and is recognized as ordinary technical common sense in the field of light-emitting elements such as light-emitting thin films and inorganic EL elements. Therefore, conventionally, there has been no report on a luminescent thin film in which the concentration of the luminescent center material is set relatively high. Furthermore, it has not been reported that when the concentration of the luminescent center material is set relatively high, the luminance is higher than that of the luminescent thin film containing the luminescent center material at a concentration of several atomic percent.

  However, when the present inventors use alkaline earth metal elements, group 13 metal elements, rare earth elements and sulfur as the constituent material of the phosphor thin film, the content ratio of the rare earth elements, which are the main luminescent center materials, is conventionally increased. It was found that no decrease in luminance was observed even when the value was high. On the contrary, the present inventors have found that the brightness is improved sharply, and a much higher level of light emission brightness can be achieved as compared with the prior art. Although the cause has not been fully elucidated, the present inventors infer as follows as one of the factors. However, the factor is not limited to this.

That is, when the base material constituting the light emitter thin film according to the present invention is, for example, Ba as an alkaline earth metal element, Al as a Group 13 metal element, and Eu as a rare earth element, the crystal of BaAl ₂ S ₄ is essentially used. It is considered that a structure is formed. Then, it is presumed that Eu is arranged in a fixed state so as to replace a part of the Ba site in this crystal structure. When Eu is incorporated in the crystal structure in this way, when the Eu concentration is relatively low, there is a low probability that Eu is substituted for both adjacent Ba sites. Therefore, it is considered that concentration quenching of Eu, which is the emission center, hardly occurs. However, as the Eu concentration increases, the probability that Eu is substituted and arranged on both adjacent Ba sites increases. As a result, the frequency of occurrence of Eu concentration quenching increases, and it is estimated that the light emission luminance of the light emitter thin film decreases.

However, when the Eu concentration is further increased, BaAl ₂ S ₄ is attributed to the structural balance (ion radius, etc.) and electrical balance (maintain electrical neutrality, etc.) of each element in the phosphor thin film. In contrast, it is considered that a new crystal phase in which Eu is stably coordinated is formed from the beginning. In this new crystal phase, it is considered that Eu concentration quenching is less likely to occur due to, for example, a stable state in which Eu is coordinated at a distant position, and the emission luminance is increased.

  The light emitting thin film of the present invention has a longer light emission lifetime than that of the prior art when the material contained therein is configured as described above. This is considered to be because the above-described new crystal phase is formed and the crystal phase is superior in mechanical and chemical stability to the conventional one, but the factor is not limited to this.

  In the phosphor thin film of the present invention, the alkaline earth metal element is preferably Ba, the group 13 metal element is Al, and the rare earth element is Eu. By using such elements together as the constituent material of the light emitter thin film, the light emission luminance and the light emission lifetime tend to be further improved.

  The light-emitting element of the present invention includes one or more inorganic functional layers between electrodes facing each other, and one or more of the inorganic functional layers includes an alkaline earth metal element, a group 13 metal element, a rare earth element, and A phosphor layer containing sulfur, characterized in that the content ratio of the rare earth element to the total amount of the alkaline earth metal element and the rare earth element is 10 atomic% or more. Although the present inventors consider that such a light-emitting element solves the above-described problem is the same as the light-emitting thin film of the present invention, the factor is not limited thereto.

  Moreover, the light emitting element of this invention improves the light emission lifetime conventionally compared with the material contained in a light-emitting body layer as the above structure. This is thought to be because the new crystal phase formed by containing more rare earth elements than in the past is superior in mechanical and chemical stability to the conventional crystal phase. It is not limited.

  In the light emitting device of the present invention, it is preferable that the alkaline earth metal element contained in the phosphor layer is Ba, the group 13 metal element is Al, and the rare earth element is Eu. By simultaneously using such an element as a constituent material of the light emitting layer, the light emitting element of the present invention tends to further improve the light emission luminance and the light emission lifetime.

  According to the present invention, it is possible to provide a light-emitting thin film and a light-emitting element that can further improve the light emission luminance as compared with the prior art.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as necessary. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  The light emitting element of this embodiment is the inorganic EL element 100 shown in FIG. An inorganic EL element 100 shown in FIG. 1 is a top emission type double-insulated inorganic EL element. On a substrate 2, a lower electrode layer 3, a lower insulator layer 4, a light emitter layer 5, and an upper insulator. The layer 6 and the upper electrode layer 7 are laminated in this order. The lower insulator layer 4, the light emitter layer 5, and the upper insulator layer 6 are specific examples of the inorganic functional layer according to the present invention. The lower insulator layer 4 further includes a thick film insulator layer (first insulator layer) 42, a second insulator layer 44, and a thin film insulator layer (third insulator layer) 46 in this order from the substrate side. It is a layered product. The lower electrode layer 3 and the upper electrode layer 7 are arranged such that one is a row electrode and the other is a column electrode, and their extending directions are orthogonal to each other.

  In the inorganic EL element 100 having such a configuration, a matrix electrode is configured by the lower electrode layer 3 and the upper electrode layer 7, and the light emitter layer 5 at the intersection of the row electrode and the column electrode is a pixel. By selectively applying an AC voltage or a pulse voltage from the AC power source 9 to each pixel constituted by the matrix electrode, the luminescent layer 5 emits electroluminescence, and the emitted light is emitted from the upper insulator layer 6 and the upper electrode. The light passes through the layer 7 and is emitted to the outside. Hereinafter, the material which comprises each member of the inorganic EL element 100 is demonstrated.

(substrate)
The substrate 2 is not particularly limited as long as each layer of the inorganic EL element 100 can be formed on the upper part and there is no possibility of contaminating each layer formed above, and the substrate 2 is formed when the inorganic EL element 100 is formed. It is preferable to have heat resistance that can withstand the annealing temperature in the annealing treatment.

Specifically, the heat resistant temperature or melting point is preferably 600 ° C. or higher, more preferably 700 ° C. or higher, and still more preferably 800 ° C. or higher. As materials for substrates having such characteristics, alumina (Al ₂ O ₃ ), forsterite (2MgO · SiO ₂ ), steatite (MgO · SiO ₂ ), mullite (3Al ₂ O ₃ · 2SiO ₂ ), Ceramic substrate mainly composed of beryllia (BeO), aluminum nitride (AlN) silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), etc., and glass obtained by mixing and sintering glass powder using these ceramic material powders as fillers Examples thereof include a ceramic substrate and a crystallized glass substrate containing an alkaline earth crystallization component.

(Lower electrode layer)
The lower electrode layer 3 is disposed on the substrate 2 so that a plurality of strip electrodes extend in a certain direction in a striped manner at regular intervals. The lower electrode layer 3 expresses a predetermined high conductivity, is preferably not easily damaged by a high temperature or an oxidizing atmosphere during annealing, and further reacts with each layer formed above. It is more preferable that the property is as low as possible.

  Specifically, the material constituting the lower electrode layer 3 is preferably a metal material. For example, a noble metal such as Au, Pt, Pd, Ir, or Ag, Au—Pd, Au—Pt, Ag—Pd, or Ag— Preferred examples include a noble metal alloy such as Pt and an alloy containing a noble metal element as a main component and a base metal element such as Ag—Pd—Cu. By using these metal materials, resistance to high temperatures or oxidizing atmospheres can be sufficiently enhanced.

(Lower insulator layer)
The lower insulator layer 4 preferably has a high dielectric constant and a high breakdown voltage in order to realize an inorganic EL element that can be driven with high luminance and low voltage. As described above, the lower insulator layer 4 in the present embodiment includes the thick film insulator layer 42, the second insulator layer 44, and the thin film insulator layer 46 that are formed on the lower electrode layer 3 in this order. It is a laminated body. By forming a large portion of the lower insulator layer 4 with the thick film insulator layer 42, a high dielectric constant of 100 times or more is achieved as compared with the case where only the thin film insulator layer is used as the lower insulator layer. Is done.

The thick film insulator layer 42 is an insulator layer formed by a so-called thick film method, that is, a ceramic layer formed by firing a powdery insulator material. The constituent material of the thick film insulator layer 42 is not particularly limited. For example, BaTiO ₃ , (Ba _x Ca _1-x ) TiO ₃ , (Ba _x Sr _1-x ) TiO ₃ , PbTiO ₃ , PZT, PLZT, etc. (Perovskite) dielectric materials having a perovskite structure, composite perovskite relaxor type ferroelectric materials represented by PMN (Pb (Mg _1/3 Nb _2/3 ) O ₃ ), etc., Bi ₄ Ti ₃ O ₁₂ A bismuth layered compound typified by SrBi ₂ Ta ₂ O ₉ or the like, or a tungsten bronze ferroelectric material typified by (Sr _x Ba _1-x ) Nb ₂ O ₆ or PbNb ₂ O ₆ is preferably used.

Among these, a ferroelectric material having a perovskite structure such as BaTiO ₃ , PZT, and PMN is more preferable from the viewpoint that a higher dielectric constant can be achieved and firing is relatively easy. A dielectric material containing lead atoms therein is particularly preferred. Such a dielectric material containing lead has a melting point of lead oxide as low as 888 ° C., and lead oxide and other oxide-based materials (for example, SiO ₂ , CuO, Bi ₂ O ₃ , Fe ₂ O _3, etc.) Since a liquid phase is formed at a low temperature of about 600 to 800 ° C. between them, firing at a low temperature is simplified by using an appropriate sintering aid, and an extremely high dielectric constant is exhibited.

As such a dielectric material containing lead, for example, a perovskite structure dielectric material such as PZT or PLZT (PbZrO ₃ —PbTiO ₃ solid solution added with La), PMN (Pb (Mg _1/3 Nb _2/3 ) O ₃ ), a composite perovskite relaxor-type ferroelectric material, and a tungsten bronze-type ferroelectric material typified by PbNb ₂ O ₆ can be preferably used. These can easily form a dielectric layer having a relative dielectric constant of 1000 or more at a firing temperature of around 800 ° C., and particularly when a complex perovskite relaxor type ferroelectric material such as PMN is used, the relative dielectric constant is 10,000. It is also possible to obtain a dielectric exhibiting a high dielectric constant exceeding.

  The second insulator layer 44 formed on the above-described thick film insulator layer 42 is a layer for covering the surface of the thick film insulator layer 42. The dielectric constant is desirably as high as possible, and the relative dielectric constant is preferably 100 or more, more preferably 500 or more. Examples of the dielectric material exhibiting such a high dielectric constant include the same types of materials as those suitably used for the thick film insulator layer 42 described above. Further, the film thickness of the second insulator layer 44 may be such a thickness that the minute unevenness present on the surface of the thick film insulator layer 42 is sufficiently embedded.

  The thin-film insulator layer 46 formed on the second insulator layer 44 and the upper insulator layer 6 formed on the light emitter layer 5 described later facilitate the control of the electronic state at both side interfaces of the light emitter layer 5. In order to stabilize the electron injection into the luminous body layer 5 and increase its efficiency. Since the thin-film insulator layer 46 and the upper insulator layer 6 are symmetrically arranged with the light emitter layer 5 as the center, the electronic states at both interfaces of the light emitter layer 5 become symmetrical, so that AC driving is performed. The positive / negative symmetry of the light emission characteristics at the time is improved. The thin film insulator layer 46 and the upper insulator layer 6 do not need to have a function of ensuring the withstand voltage, and the film thickness may be relatively thin, preferably about 10 to 1000 nm, more preferably about 20 to 200 nm. It is said.

The specific resistance of the thin-film insulator layer 46 and the upper insulator layer 6 is preferably 10 ⁸ Ω · cm or more, more preferably on the order of 10 ¹⁰ to 10 ¹⁸ Ω · cm. Furthermore, the constituent materials of these layers are not particularly limited, but specifically, it is preferable that the layers are made of a substance having a relative dielectric constant of 3 or more. As such a constituent material, for example, silicon oxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), tantalum oxide (Ta ₂ O ₅ ), yttrium oxide (Y ₂ O ₃ ), zirconia (ZrO ₂ ), silicon Examples thereof include oxynitride (SiON) and alumina (Al ₂ O ₃ ).

(Phosphor layer)
The light emitter layer 5 is an example of the light emitter thin film of the present invention, and contains an alkaline earth metal element, a group 13 metal element, a rare earth element, and sulfur.

  Although it does not specifically limit as an alkaline-earth metal element used for the light-emitting body layer 5, From a viewpoint of obtaining higher EL characteristics (a brightness | luminance, light emission lifetime, a drive voltage, color purity, etc.) with sufficient balance, Mg, Ca, Sr, and Ba It is preferably one or more elements selected from the group consisting of, and more preferably Ba.

  Although it does not specifically limit as a 13 group metal element used for the light-emitting body layer 5, From the viewpoint similar to the above, it is preferable in it being 1 or more types of elements chosen from the group which consists of Al, B, Ga, and In, Al or Ga is more preferable, and Al is particularly preferable.

  The above-described elements and sulfur (S) mainly constitute the base material of the light emitting layer 5. The combination of these elements is not particularly limited, but from the viewpoint of further improving the luminance, barium thioaluminate combining Ba, Al and S, strontium thiogallate combining Sr, Ga and S, Ca, Ga and S Calcium thiogallate combined with strontium thioindate combined with Sr, In and S is preferable, and barium thioaluminate is more preferable.

  The composition ratio (content ratio) of these elements may be a stoichiometric ratio for obtaining a stable crystal structure, but is not particularly limited. Therefore, for example, when barium thioaluminate is used as a base material, the composition ratio of each element is a stoichiometric ratio of Ba: Al: S = 1: 2: 4 (atomic ratio; the same applies hereinafter), 2: 2 : 5 or 1: 4: 7, or some deviation from such an atomic ratio.

  The rare earth element used in the light emitting layer 5 mainly functions as a light emission center. As such a rare earth element, from the same viewpoint as described above, Sc, Y, La, Ce, Pr, Nd, Gd, Tb, Ho, Er, Tm, Lu, Sm, Eu, Dy, and Yb are used. One or more selected elements are preferred.

  For example, the rare earth element combined with the barium thioaluminate matrix material is Eu for a blue phosphor, Ce, Tb, Ho for a green phosphor, Sm, Yb, Nd is preferable, and among these, it is most preferable to use Eu as a blue phosphor. Further, when a strontium thiogallate matrix material and Eu are combined, a green phosphor is obtained, and when a strontium thioindate matrix material or barium thioindate matrix material is combined with Eu, a red phosphor is obtained.

  The content ratio of the rare earth element in the phosphor layer 5 is 10 atomic% or more with respect to the total amount of the alkaline earth metal element and the rare earth element. By setting the content ratio of the rare earth element in such a range, the inorganic EL element 100 of the present embodiment can improve the light emission luminance. From the same viewpoint, the content ratio of the rare earth element is preferably 10 to 90 atomic%, more preferably 12 to 75 atomic%, and further preferably 14 to 50 atomic%.

  In addition, it is preferable that the phosphor layer 5 contains some oxygen (O). This can further prevent the light emission life (driving life) from decreasing with time. This is probably because the presence of the oxide component having excellent oxidation resistance in the phosphor layer 5 sufficiently prevents contact between the sulfide component and oxygen in the air, but the factor is limited to this. Not. It is preferable that the content ratio of oxygen in the luminous body layer 5 is about 5 to 30 atomic% with respect to the sulfur component (S), since it is possible to further suppress the emission lifetime over time.

  Each element described above may exist in an ionic state in the luminescent layer 5 or may exist in an atomic state. Further, the light emitting layer 5 may be a single crystal layer or a crystal layer in which two or more materials are mixed, an amorphous layer, or a state in which they are mixed.

  The film thickness of the light emitter layer 5 is not particularly limited as long as good light emission characteristics can be obtained. However, if the film thickness is too thick, the driving voltage increases, and if it is too thin, the light emission efficiency tends to decrease. Therefore, this film thickness is preferably about 100 to 2000 nm, more preferably about 150 to 1000 nm.

(Upper electrode layer)
The upper electrode layer 7 is disposed on the upper insulator layer 6 so that a plurality of strip electrodes extend in a planar direction perpendicular to the extending direction of the lower electrode layer 3 in a striped manner at regular intervals. Yes. The upper electrode layer 7 is made of a transparent conductive material because the inorganic EL element 100 is a top emission type. As such a transparent conductive material, an oxide conductive material such as In ₂ O ₃ , SnO ₂ , ITO, or ZnO—Al can be used. The thickness of the upper electrode layer 7 is preferably 0.2 to 1 μm from the viewpoint of sufficiently reducing the specific resistance.

  The material composition constituting each of the above-described layers can be confirmed by fluorescent X-ray analysis (XRF), X-ray photoelectron analysis (XPS), TEM-EDS (Transmission Electronicroscopy-Energy Dispersive X-ray Spectroscopy), or the like.

  The inorganic EL element 100 of the present embodiment described above can further improve the light emission luminance as compared with the related art. For example, the following factors can be considered.

That is, in the light emitting layer of the inorganic EL element according to the present embodiment, when the Eu concentration is increased as compared with the conventional case, the structural balance (ion radius, etc.) and the electrical balance (electrical medium) of each element in the light emitting thin film. It is considered that a new crystal phase in which Eu is stably coordinated from the beginning is formed, which is different from BaAl ₂ S _{4 and the} like. In this new crystal phase, it is considered that Eu concentration quenching is less likely to occur due to, for example, a stable state in which Eu is coordinated at a distant position, and the emission luminance is increased.

  In addition, the inorganic EL element 100 of the present embodiment has a longer light emission lifetime than the conventional one. This is because the above-described new crystal phase formed by containing more rare earth elements than the conventional one has better mechanical and chemical stability than the crystal phase in the conventional phosphor layer. However, the factor is not limited to this.

  An example of a method for manufacturing the inorganic EL element 100 configured as described above will be described below. First, a substrate 2 made of a ceramic substrate, a glass ceramic substrate, a crystallized glass substrate, or the like that has been subjected to surface polishing is prepared.

  Next, a striped lower electrode layer 3 is formed on the substrate 2. The method is not particularly limited, and can be formed using, for example, a powder metal paste, a printing method using an organic metal paste (resinate metal paste), or a commonly used etch process.

  Next, the lower insulator layer 4 is formed on the substrate on which the lower electrode layer 3 is formed. In this step, first, the thick insulator layer 42 is formed, and then the second insulator layer 44 is formed thereon by a solution coating firing method. Then, a thin film insulator layer 46 is formed thereon by vapor deposition. As the vapor deposition method, a PVD method (physical vapor deposition method) such as a sputtering method or a vapor deposition method or a CVD method (chemical vapor deposition method) can be preferably used.

  Specific methods for forming the thick film insulator layer 42 include the following methods. First, a thick film paste prepared by previously mixing a ceramic material powder with a binder, a dispersant, a solvent, and the like is applied onto the substrate 2 and dried to form a thick film green. Next, this thick film green is fired at a predetermined temperature to form an insulator layer. Alternatively, a solution coating firing method such as a sol-gel method or a MOD (Metallo-Organic Decomposition) method may be used.

  The solution coating and baking method used when forming the second insulator layer 44 is to apply a precursor solution of an insulator material for forming the second insulator layer 44 on the thick film insulator layer 231. In this method, the second insulating layer 44 is obtained by firing the coating film. Examples of the solution coating and baking method include a sol-gel method and a MOD (Metallo-Organic Decomposition) method.

  In the sol-gel method, generally, a predetermined amount of water is added to a metal alkoxide dissolved in a solvent, followed by hydrolysis and polycondensation reaction to obtain a thick sol precursor solution having MOM bond in the molecule. In this method, the second insulator layer 44 is formed by coating on the film insulator layer 42 and baking the coating film. The MOD method is a method in which a precursor solution prepared by dissolving a metal salt of a carboxylic acid having an MO bond in an organic solvent is applied onto the thick film insulator layer 42 and the coating film is baked. The second insulator layer 44 is formed by the above method. 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.

  These sol-gel method and MOD method are not completely separate methods but are generally used in combination with each other. For example, when forming a thin film made of PZT, a solution can be prepared using lead acetate as a Pb source and using the metal alkoxide as a Ti or Zr source.

  Alternatively, the two methods of the sol-gel method and the MOD method may be collectively referred to as the sol-gel method. In either case, the second insulator is obtained by applying the precursor solution on the thick film insulator layer 42 and baking it. Since the layer 44 is formed, in the present invention, both methods are collectively referred to as “solution coating firing method”. In the present invention, the “precursor solution” also includes a solution in which submicron-sized insulator particles and an insulator precursor solution are mixed, and the solution is applied onto the thick film insulator layer 42. The method of firing is also included in the solution coating firing method.

  When such a solution coating / firing method is used, the insulator compound constituting the second insulator layer 44 is uniformly mixed on the order of submicron or less in both the sol-gel method and the MOD method. With this process, a dense insulator can be synthesized. Further, when the solution coating and baking method is used, a step of applying and baking the precursor solution is performed, so that even if there are minute irregularities on the thick film insulator layer 42, the second insulation formed on the depressions. The body layer 44 is relatively thick, and conversely, the second insulator layer 44 formed on a portion (convex portion) other than the concave portion is relatively thin.

  In addition, in order to obtain the second insulator layer 44 by a single application and baking by a solution coating and baking method, a film forming aid comprising a polyhydric alcohol in the precursor solution or a polymer organic material having a polar group in the molecule. May be added. If it carries out like this, it can be easy to form the 2nd insulator layer 44 of thickness 0.5-1 micrometer by one application | coating baking. Examples of such film forming aids include alkane diols such as 1,3-propanediol and neopentyl glycol, glycols such as polyethylene glycol and polypropylene glycol, or polyvinyl pyrrolidone, polyvinyl acetamide, and hydroxypropyl cellulose. And polar polymers.

Next, the phosphor layer 5 is formed on the lower insulator layer 4 by EB vapor deposition or sputtering using a target obtained by processing the material constituting the phosphor layer 5 into a pellet shape. Specifically, for example, when the phosphor layer 5 made of BaAl ₂ S ₄ : Eu is formed by EB deposition, each pellet of Al sulfide and Ba sulfide added with Eu is prepared, and H _{2 is formed.} EB vapor deposition is performed on the lower insulator layer 4 using these two pellets as targets in a chamber into which S gas has been introduced. Eu to be added may be in the form of metal, oxide, fluoride, or sulfide.

  Moreover, after forming the light emitting layer 5 in this way, it is preferable to perform an annealing treatment. The annealing treatment may be performed immediately after the formation of the light emitter layer 5, that is, with the light emitter layer 5 exposed, or may be performed after the upper insulator layer 6 or the upper electrode layer 7 is formed. The annealing treatment can be performed in the air, in a nitrogen atmosphere, in an argon atmosphere, in a sulfur vapor atmosphere, in a hydrogen sulfide atmosphere, or in an oxygen atmosphere, and is preferably performed in an oxidizing atmosphere. The ambient pressure at this time is appropriately selected from high vacuum to atmospheric pressure.

  Here, the oxidizing atmosphere refers to a state where the oxygen concentration is equal to or higher than that of air. By performing the annealing in an oxidizing atmosphere, crystallization of the phosphor layer 5 is promoted, and the light emission luminance can be further improved. The annealing temperature is usually in the range of 500 to 1000 ° C, and preferably in the range of 600 to 800 ° C. Furthermore, the annealing time is usually about 1 to 60 minutes, preferably 5 to 30 minutes. When the annealing temperature is lower than 500 ° C. or the annealing time is less than 1 minute, it tends to be difficult to sufficiently improve the light emission luminance. When the annealing temperature is higher than 1000 ° C. or the annealing time exceeds 60 minutes In some cases, components other than the light emitter layer 5 in the inorganic EL element 100 may be damaged.

  Next, after forming the upper insulator layer 6 on the light emitting layer 5 in the same manner as the formation of the thin film insulator layer 46, the striped upper electrode layer 7 is formed thereon by vapor deposition, sputtering, CVD, The inorganic EL element 100 is obtained by a known method such as a sol-gel method or a printing and baking method.

  As mentioned above, although preferred embodiment concerning this invention was described, this invention is not limited to the said embodiment.

For example, in another embodiment of the inorganic EL element of the present invention, a barrier layer containing ZnS as a constituent material may be provided on one side or both sides of the phosphor layer 5 as the inorganic functional layer. The constituent material of the light emitting layer 5 described above is a light emitting material in which oxygen is relatively easily taken up. Therefore, by providing such a barrier layer, it is possible to prevent oxygen (O) in the insulator layer and / or the atmosphere from being mixed into the light emitting material during annealing. Thereby, since mixing of O into a light emitting material such as BaAl ₂ S ₄ can be sufficiently suppressed, an inorganic EL element that emits light of a desired color can be obtained.

  Such a barrier layer also serves as a carrier injection layer. Thereby, the electron injection to the light emitting layer is enhanced, and as a result, the light emission luminance and light emission efficiency of the inorganic EL element are improved. In addition, since the electron injection is facilitated, the voltage for generating effective light emission (the light emission threshold voltage in the curve indicating the luminance-voltage characteristic (LV curve)) is reduced, and the characteristic curve is steep. Therefore, the load on the drive circuit element can be reduced and the power consumption can be reduced.

  Further, another layer other than the barrier layer may be further disposed between the above-described layers of the inorganic EL element. As another layer, there is a layer having a configuration for increasing the adhesion between the adjacent layers described above, or a layer having a configuration for relieving stress generated between the adjacent layers during driving. Can be mentioned.

  In the inorganic EL element of the present invention, the lower insulator layer may not have the three-layer structure as described above, and may be composed of only one or two layers, and four or more insulating layers You may be comprised with the body layer.

  Furthermore, in the inorganic EL device according to another embodiment of the present invention, a plurality of light emitting layers may be formed. In that case, the plurality of light emitting layers may be stacked so as to overlap each other, or may be stacked with an electrode layer interposed therebetween. Alternatively, the light emitter layer may be formed so as to be aligned in the crossing direction of the film thickness direction. In these cases, one of the plurality of light emitter layers may be the same light emitter layer as described above. Therefore, for example, when the inorganic EL element of the present invention is used for an RGB color display, the blue light emitting layer is the same as the light emitting layer described above, and the red light emitting layer is known such as ZnS: Mn, CaS: Eu. And using a known green light emitting material such as ZnS: Tb and CaS: Ce as a green light emitting layer. By doing so, a blue light emitting layer that has conventionally had a lower luminance than other light emitting color light emitting layers according to the present invention, the luminance of the blue light emitting layer is sufficiently improved, and RGB A color display excellent in balance can be obtained.

  In addition, the phosphor thin film of the present invention can be used not only as a phosphor layer of an inorganic EL element but also as a phosphor layer provided in a display using other light emitting elements such as PDP and FED. Thereby, a display excellent in blue color development can be formed.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

Example 1
An inorganic EL element 50, which is a light-emitting element having a structure as shown in the schematic perspective view of FIG. 2, was produced by the following procedure. First, Au in the form of a powder metal paste was screen-printed on an alumina substrate 52 of 99.6% purity, and baked at 850 ° C. for 20 minutes in the air atmosphere to form a lower electrode layer 53 having a thickness of 1 μm.

Next, PMN-PT was used as a material for the thick film insulator layer, which was powdered and then added with PbO-CuO as a sintering aid, ethyl cellulose as a binder, α-terpineol as a solvent, and further unsaturated. A fatty acid dispersant and a phthalate ester plasticizer were mixed to form a thick film paste, which was applied onto the substrate 52 on which the lower electrode layer 53 was formed to form a coating film. Subsequently, the coating film was dried at 150 ° C. for 10 minutes, and further baked at 850 ° C. for 20 minutes in the air atmosphere to form a thick film insulator layer 542 having a thickness of 20 μm. Next, a thin film insulator layer 546 having a thickness of 20 nm, which is made of Al ₂ O _3, is formed on the thick film insulator layer 542 by an evaporation method using Al ₂ O ₃ pellets as an evaporation source, and the lower insulation is formed. A body layer 54 was obtained. Further thereon, a barrier layer 581 containing ZnS as a constituent material was formed by a vapor deposition method using ZnS pellets as a vapor deposition source to obtain a laminate.

Next, the laminate after the above-described barrier layer 581 was formed was placed in a vacuum chamber having an EB source of BaS pellets to which Eu was added at a predetermined concentration and an EB source of Al ₂ S ₃ powder. Next, H ₂ S gas is introduced into the vacuum chamber at a flow rate of ₂ sccm, the reaction gas as a raw material is simultaneously evaporated from each EB source, and the lower barrier layer 581 is rotated while rotating the laminated body heated to 425 ° C. A light-emitting layer 55 containing BaAl ₂ S ₄ : Eu as a constituent material was formed thereon. Note that the EB deposition conditions were adjusted so that the film formation rate of the phosphor layer 55 was 0.5 nm / second. The film thickness of the obtained phosphor layer 55 was 250 nm. In addition to Ba, Al, S, and Eu, the phosphor layer 55 also contained oxygen (O) derived from oxygen gas in the tank. The composition of each element in the phosphor layer 55 and the Eu content ratio (Eu / (Ba + Eu)) with respect to the total amount of Ba and Eu are Ba: Al: S: O: Eu = 11.9: 29. 7: 51.7: 4.7: 2.0, and Eu / (Ba + Eu) = 14 atomic%.

  Next, an upper barrier layer 582 having a thickness of 100 nm is formed on the phosphor layer 55 in the same manner as the lower barrier layer 581, and an upper insulator layer 56 is formed on the upper barrier layer 582 in the same manner as the thin film insulator layer 546. did. Further, the laminated body obtained by forming the upper insulator layer 56 was subjected to an annealing treatment at 700 ° C. for 10 minutes in the air atmosphere. Then, an upper electrode layer 57 made of ITO is formed on the annealed upper insulator layer 56 by RF magnetron sputtering using an ITO target, and the lower electrode layer 53 and the upper electrode layer 57 are read. The inorganic EL element of Example 1 was obtained by connecting with a wire.

(Example 2)
An inorganic EL element of Example 2 was obtained in the same manner as Example 1 except that the Eu concentration in the BaS pellet was changed. The composition of each element and Eu / (Ba + Eu) in the light-emitting layer of the obtained device are Ba: Al: S: O: Eu = 10.6: 30.6: 51.4: 5.0 in atomic ratio. 2.4, Eu / (Ba + Eu) = 19 atomic%.

(Comparative Example 1)
An inorganic EL element of Comparative Example 1 was obtained in the same manner as in Example 1 except that the Eu concentration in the BaS pellet was changed. The composition of each element and Eu / (Ba + Eu) in the light-emitting layer of the obtained device are Ba: Al: S: O: Eu = 12.5: 29.5: 52.5: 4.3 by atomic ratio. 1.3, Eu / (Ba + Eu) = 9.4 atomic%.

(Comparative Examples 2 to 5)
Inorganic EL elements of Comparative Examples 2 to 5 were obtained in the same manner as in Example 1 except that the Eu concentration in the BaS pellet was changed. The composition of each element and Eu / (Ba + Eu) in the phosphor layer of the obtained device were as shown in Table 1.

<Emission luminance evaluation>
Between both electrodes of the inorganic EL elements of Examples 1 and 2 and Comparative Examples 1 to 5, modulation voltage: 100-250 Vp, drive frequency: 120 Hz, applied voltage waveform: pulse (pulse width: 50 μsec), measurement environment temperature: 23 An AC voltage was applied under the condition of ° C., and the light emission luminance at each voltage was measured. The light emission luminance to be compared is a voltage obtained by applying 60 V from the light emission threshold voltage, where the voltage at which light emission of 1 cd / m ² can be obtained in each EL element is obtained (hereinafter referred to as “L60”). The light emission luminance is used. In addition, the numerical value of luminance is expressed as relative intensity with the luminance of L60 as 1 for the EL element of Comparative Example 2. The results are shown in Table 1, and the correlation of luminance with Eu / (Ba + Eu) is shown in FIG. In FIG. 3, rhombus plots 201, 202, 203, 204, 205, 206, and 207 show the results of Examples 1 and 2 and Comparative Examples 1, 2, 3, 4, and 5, respectively.

<Emission life evaluation>
For the inorganic EL elements of Example 1 and Comparative Examples 1 and 2, an alternating voltage was applied under the conditions of driving voltage: 180 Vp, driving frequency: 1 kHz, applied voltage waveform: pulse (pulse width: 50 μsec), measurement environment temperature: 23 ° C. Then, the change with time of the emission luminance was measured. The numerical value of the luminance was relatively expressed with the luminance at the beginning of voltage application (0 hours) as 1. The results are shown in FIG. In FIG. 4, a solid line 301, a two-dot chain line 302, and a dotted line 303 indicate the results of Example and Comparative Examples 1 and 2, respectively.

It is a schematic perspective view which shows the principal part of the light emitting element which concerns on embodiment of this invention. It is a schematic perspective view which shows the principal part of the inorganic EL element which concerns on an Example. It is a graph which shows the correlation of the brightness | luminance with respect to Eu / (Ba + Eu) in the light-emitting body layer in the inorganic EL element which concerns on an Example. It is a graph showing the light emission lifetime of the inorganic EL element which concerns on an Example. It is a schematic perspective view which shows the principal part of the typical structure of the conventional inorganic EL element.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Board | substrate, 3 ... Lower electrode, 4 ... Lower insulator layer, 5 ... Light-emitting body layer, 6 ... Upper insulator layer, 7 ... Upper electrode, 100 ... Inorganic EL element.

Claims (8)

  Alkaline earth metal element containing at least Ba, Group 13 metal element, rare earth element and sulfur are contained, and the content ratio of the rare earth element to the total amount of the alkaline earth metal element and the rare earth element is 10 atomic% or more and 19 A light emitter thin film characterized by being at most atomic%.   Alkaline earth metal element, Group 13 metal element, rare earth element and sulfur are contained, and the content ratio of the rare earth element to the total amount of the alkaline earth metal element and the rare earth element is 14 atomic% or more and 19 atomic% or less. A phosphor thin film characterized by being.   3. The light emitter thin film according to claim 1, wherein the alkaline earth metal element is Ba, the group 13 metal element is Al, and the rare earth element is Eu.   The phosphor thin film according to any one of claims 1 to 3, further comprising oxygen and having an oxygen content ratio of 5 to 30 atomic% with respect to sulfur. One or more inorganic functional layers are provided between the electrodes facing each other,
One or more of the inorganic functional layers is a light emitting layer containing an alkaline earth metal element containing at least Ba, a group 13 metal element, a rare earth element and sulfur,
A light-emitting element, wherein a content ratio of the rare earth element to a total amount of the alkaline earth metal element and the rare earth element is 10 atomic% or more and 19 atomic% or less. One or more inorganic functional layers are provided between the electrodes facing each other,
One or more of the inorganic functional layers is a phosphor layer containing an alkaline earth metal element, a group 13 metal element, a rare earth element and sulfur,
The light-emitting element, wherein a content ratio of the rare earth element to a total amount of the alkaline earth metal element and the rare earth element is 14 atomic% or more and 19 atomic% or less.   The light emitting device according to claim 6, wherein the alkaline earth metal element is Ba, the group 13 metal element is Al, and the rare earth element is Eu. The light emitting layer further includes oxygen, and the content ratio of oxygen, according to any one of claims 5-7, characterized in that those 5 to 30 atomic% with respect to sulfur Light emitting element.

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