JP3590986B2 - Electroluminescence element - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an electroluminescence (EL) element used for, for example, a self-luminous segment display or a matrix display of instruments, or a display of various information terminal instruments.
[0002]
[Prior art]
An EL element utilizes a phenomenon of emitting light when an electric field is applied to a phosphor such as ZnS (zinc sulfide), and has been attracting attention as a component of a self-luminous display. FIG. 7 is a schematic diagram showing a typical conventional cross-sectional structure of an EL element. The EL element 10 has a first electrode 2 made of an optically transparent ITO film, a first insulating layer 3 made of Ta ₂ O ₅ (tantalum pentoxide), and a light emitting layer on a glass substrate 1 which is an insulating substrate. 4, a second insulating layer 5 and a second electrode 6 made of an ITO film are sequentially laminated. The ITO (Indium Tin Oxide) film is a transparent conductive film obtained by adding Sn (tin) to In ₂ O ₃ (indium oxide) and has a low resistivity, and thus has been widely used for a transparent electrode. The light emitting layer 4 is made of, for example, ZnS 2 as a base material, Mn (manganese), Sm (samarium), or Tb (terbium) added as a luminescent center, or SrS (strontium sulfide) as a base material, and Ce as a luminescent center. (Cerium) is used. The emission color of the EL element is determined by the type of the additive in ZnS. For example, the emission center is yellow-orange when Mn is added, red when Sm is added, and green when Tb is added. Is obtained. When Ce is added to SrS as a luminescent center, a blue-green luminescent color is obtained.
[0003]
[Problems to be solved by the invention]
A ZnS: Sm light emitting layer has been developed as an EL light emitting layer that emits red light, but sufficient luminance has not been obtained. On the other hand, a phosphor such as Y ₂ O ₃ : Eu (europium-activated yttrium oxide), which has conventionally been used as a red phosphor of a cathode ray tube of a color television, has a base material that is not necessarily a semiconductor. It does not always emit light efficiently and has not been put to practical use. ZnGa ₂ S ₄ : Mn (manganese-activated gallium sulfide) is a phosphor which emits red light and whose base material is a semiconductor, is disclosed in Japanese Patent Application Laid-Open No. 55-147584, CdGa ₂ S ₄ : Mn (manganese-activated sulfur). Gallium cadmium) is disclosed in JP-B-61-4433. The crystal system of these host materials is tetragonal. However, when a ZnGa ₂ S ₄ : Mn phosphor was prepared as the EL light emitting layer, red light emission could not be recognized. Also, since CdGa ₂ S ₄ : Mn phosphor contains Cd, it is not a very desirable material from an industrial and environmental point of view.
[0004]
For this reason, a method of obtaining red EL light emission by using a filter that transmits only a red component in a ZnS: Mn light emitting layer that emits yellow-orange light but has high luminance is used widely. However, the necessity of the filter causes problems such as an increase in cost, a decrease in the viewing angle, and a complicated configuration of the EL display.
[0005]
The present invention has been made to solve the above-described problem, and an object of the present invention is to use Mn as an emission center and to select an appropriate substance as a base material of a light-emitting layer, so that a filter is interposed. Another object of the present invention is to provide a novel EL device which emits red light without any problem.
[0006]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, an EL device according to the present invention has a light-emitting layer in which a sulfur compound to which Mn is added as an activator, and a crystal system of the sulfur compound is orthorhombic or cubic. And S (sulfur) is coordinated around an element X having a valence of +2 among the constituent elements of the sulfur compound, and the bond distance of XS is not less than 2.56Å and not more than 2.75Å. Or the light-emitting layer is a sulfur compound using Mn as an activator, and the crystal system of the sulfur compound belongs to one of the orthorhombic system or the cubic system, and the constituent elements of the sulfur compound It suffices that four S (sulfur) coordinates around the element X having a valence of +2 and the bond length of XS is 2.15 to 2.27 . Specifically, MgIn ₂ S ₄ ( indium magnesium sulfide ) , MgY ₂ S ₄ (yttrium magnesium sulfide ) or TiZr ₂ S ₄ ( zirconium titanium sulfide ) is used.
[0007]
[Action and effect of the invention]
In the light emitting layer of the EL device according to the present invention, when six S (sulfur) are coordinated around the element X having a valence of +2, the bonding distance of X—S is also six S (surrounding). A base material shorter than the bonding distance of Ca-S coordinated with sulfur (2.84 °) is used. Further, when four S (sulfur) are coordinated around the element X having a valence of +2, the bonding distance of X-S is the same as that of Zn-S in which four S (sulfur) are coordinated around. A base material shorter than the bonding distance of 2.34 ° is used. Since Mn having a valence of +2 replaces the element X, the bonding distance of Mn-S in the light-emitting layer of the EL device according to the present invention is expressed as Mn-S bond distance in the CaS: Mn light-emitting layer, or ZnS: It is shorter than the Mn-S bond distance in the Mn light emitting layer. Then, the interaction between the crystal field formed by S (sulfur) and +2 valent Mn becomes stronger, the luminescence level energy is reduced, and the peak wavelength of the luminescence spectrum is CaS: Mn luminescent layer or ZnS: Mn luminescence. The light emission peak wavelength of the layer shifts to a longer wavelength side than 590 nm. This corresponds to the shift of the emission color from yellow-orange to red, and therefore, the emission layer of the EL device according to the present invention exhibits a red color with Mn as the emission center. Since this light emitting layer uses Mn as a light emission center, higher light emission luminance can be obtained as compared with Sm or the like. Further, usually, a sulfur compound is a semiconductor having a wide band gap, and thus is suitable as a base material of an EL light emitting layer. As described above, according to the EL element of the present invention, red light emission can be obtained without passing through a filter.
[0008]
【Example】
(First embodiment)
Hereinafter, the present invention will be described based on specific examples. FIG. 1 is a schematic cross-sectional view showing a cross section of a thin film EL device 100 according to the present invention. The external structure is the same as that of the conventional structure shown in FIG. Note that light is also extracted in the direction of the arrow in the EL element 100 of FIG.
[0009]
The thin film EL element 100 is formed by sequentially laminating the following thin films on a glass substrate 11 which is an insulating substrate. That is, a first transparent electrode (first electrode) 12 made of optically transparent ZnO (zinc oxide) and a first insulating material made of optically transparent Ta ₂ O ₅ (tantalum pentoxide) are formed on a glass substrate 11. A layer 13, a light-emitting layer 14 made of MgIn ₂ S ₄ (indium magnesium sulfide) to which Mn is added as a light-emitting center, a second insulating layer 15 made of optically transparent Ta ₂ O ₅ , made of optically transparent ZnO 2 A second transparent electrode (second electrode) 16 is formed.
[0010]
A method for manufacturing the thin film EL device 100 will be described below.
(1) First, a first transparent electrode 12 was formed on a glass substrate 11. As a vapor deposition material, Ga ₂ O ₃ (gallium oxide) was added to ZnO powder, mixed and formed into a pellet, and an ion plating device was used as a film forming device. Specifically, the inside of the ion plating apparatus was evacuated while maintaining the temperature of the glass substrate 11 constant. Thereafter, Ar (argon) gas was introduced to keep the pressure constant, and the beam power and the high-frequency power were adjusted so that the film formation rate was in the range of 6 to 18 nm / min.
(2) Next, a first insulating layer 13 made of Ta ₂ O ₅ was formed on the first transparent electrode 12 by a sputtering method. Specifically, the temperature of the glass substrate 11 was kept constant, a mixed gas of Ar and O ₂ (oxygen) was introduced into the sputtering apparatus, and the film was formed with a high frequency power of 1 KW.
(3) Next, a MgIn ₂ S ₄ : Mn light emitting layer 14 containing MgIn ₂ S ₄ (indium magnesium sulfide) as a base material and Mn added as a light emission center is formed on the first insulating layer 13 by a sputtering method. Formed. Specifically, the temperature of the glass substrate 11 is kept constant at 50 to 300 ° C., Ar gas is introduced into the sputtering apparatus, and a MgIn ₂ S ₄ : Mn powder target or a sintered target is used as a sputtering target. Film formation was performed at a high frequency power of 200 W. Here, the amount of Mn charged in the sputter target was adjusted such that the Mn concentration in the MgIn ₂ S ₄ : Mn light emitting layer was in the range of 0.1 to 1.0 at%. Thereafter, heat treatment was performed in a high-temperature atmosphere of 550 ° C. or more for 4 to 40 hours.
(4) Next, a second insulating layer 15 made of Ta ₂ O ₅ was formed on the light emitting layer 14 in the same manner as the first insulating layer 13 described above. Then, a second transparent electrode 16 made of a ZnO film was formed on the second insulating layer 15 by the same method as that for the first transparent electrode 12 described above.
[0011]
The thickness of each layer is 300 nm for the first transparent electrode 12 and the second transparent electrode 16, 400 nm for the first insulating layer 13 and the second insulating layer 15, and 600 nm for the light emitting layer 14. The thickness of each layer is described with reference to the central portion.
[0012]
According to the X-ray diffraction data, the parent material MgIn ₂ S ₄ (indium magnesium sulfide) of the light-emitting layer 14 formed by the above film formation method belongs to a cubic system, has an inverse spinel structure, and has a lattice constant of 10.7 °. Was confirmed. The element having a valence of +2 in this base material is Mg, and six S (sulfur) are coordinated around the element, and the bond distance of Mg-S is about 2.68 °. It was confirmed by the EXAFS (Extended X-ray Absorption Fine Structure) method. FIG. 2 shows a state in which six S (sulfur) are coordinated around Mg (indicated by element X). This bonding distance is shorter than the Ca-S bonding distance of 2.84 ° of the CaS: Mn light emitting layer in which six S (sulfur) are similarly coordinated. Accordingly, the interaction between the crystal field formed by S (sulfur) and +2 valent Mn becomes stronger, the peak wavelength of the emission spectrum shifts to a longer wavelength side than 590 nm, and red EL emission having a peak at 〜650 nm is obtained. . FIG. 3 shows the emission spectrum of this EL device. The band gap of MgIn ₂ S ₄ is 3 to 4 eV although the exact value is not known, and the value is appropriate as a base material of the EL light emitting layer.
[0013]
The matrix material of MgIn ₂ S ₄ (indium magnesium sulfide) of the first embodiment has another secondary advantage. It is based on the fact that a substance called MnIn ₂ S ₄ (indium manganese sulfide) exists, which belongs to a cubic system, has an inverse spinel structure, and has a lattice constant of 10.715 ± 8 °. That is, since MgIn ₂ S ₄ and MnIn ₂ S ₄ have the same crystal structure and their lattice constants are very close values, even if Mn is added to MgIn ₂ S ₄ , the lattice is hardly distorted, and the crystallinity of the base material is low. Can produce very good phosphors. Then, the concentration of the non-radiative recombination center, which is harmful to EL light emission, is significantly reduced. Further, scattering of carriers traveling in the light emitting layer is reduced, and it becomes easy to accelerate the carriers to high energy. Therefore, a large EL light emission luminance can be obtained as compared with the case where Sm having an ionic radius considerably different from that of Zn is added to ZnS 2.
[0014]
In forming the MgIn ₂ S ₄ : Mn light emitting layer 14, a metal organic chemical vapor deposition (MOCVD) method can be used. Specifically, the glass substrate 11 is kept at a constant temperature of 500 ° C., and the film formation chamber is placed under a reduced pressure atmosphere, and then Mg (C ₁₁ H ₂₀ O ₂ ) ₂ (dipivalo) is used using an Ar carrier gas. Similarly, using an Ar carrier gas, In (C ₂ H ₅ ) ₃ (triethylindium) and H ₂ S (hydrogen sulfide) diluted with an Ar gas are introduced into the film formation chamber. Further, in order to add a luminescence center element, Mn (C ₅ H ₅ ) ₂ (CO) ₃ (tricarbonylcyclopentadienyl manganese) is evaporated in an Ar carrier gas and supplied to a film forming chamber. By reacting and thermally decomposing these source gases, a MgIn ₂ S ₄ : Mn light emitting layer 14 to which Mn is added as a light emitting center is formed.
[0015]
(Second embodiment)
In the second embodiment of the present invention, a first transparent electrode (first electrode) 12 made of ZnO (zinc oxide) and a first transparent electrode made of Ta ₂ O ₅ are sequentially formed on a glass substrate 11 of the EL element 100 in FIG. After forming the insulating layer 13, a light emitting layer 14 made of MgY ₂ S ₄ (yttrium magnesium sulfide) with Mn added as a light emitting center is formed. Thereafter, the formation of the second insulating layer 15 and the second transparent electrode 16 is the same as in the first embodiment.
[0016]
The light-emitting layer 14 is maintained at a constant temperature of 50 to 300 ° C. of the glass substrate 11, introduces Ar gas into a sputtering apparatus, and uses a MgY ₂ S ₄ : Mn powder target or a sintered target to generate 200 W It was formed by sputtering with high frequency power. Here, the amount of Mn charged in the sputter target was adjusted so that the Mn concentration in the MgY ₂ S ₄ light emitting layer was in the range of 0.1 to 1.0 at%. Thereafter, heat treatment was performed in a high-temperature atmosphere of 550 ° C. or more for 4 to 40 hours.
[0017]
Based on the X-ray diffraction data, the parent MgY ₂ S ₄ of the light-emitting layer 14 formed by the above film formation method belongs to the orthorhombic system, and has a lattice constant of a = 12.60 °, b = 12.73 °, and c. = 3.77 °. In this base material, the element having a valence of +2 is Mg, around which four S (sulfur) are coordinated, and the bond distance of Mg-S is up to 2.15 °. This was confirmed by the EXAFS method. This bond distance is shorter than the Zn-S bond distance of 2.34 ° of the ZnS: Mn light emitting layer in which four S (sulfur) are similarly coordinated. Therefore, the interaction between the crystal field formed by S (sulfur) and +2 valent Mn becomes strong, the peak wavelength of the emission spectrum shifts to a longer wavelength side than 590 nm, and red EL emission having a peak at about 700 nm is obtained. .
[0018]
The host material of the second embodiment also has the same secondary advantages as in the first embodiment. There is a substance called MnY ₂ S ₄ (yttrium manganese sulfide), which belongs to the same space group of the orthorhombic system, and has lattice constants a = 12.62 °, b = 12.75 °, c = 3.78 °. This is because it has a value very close to
[0019]
(Third embodiment)
In the third embodiment of the present invention, a first transparent electrode (first electrode) 12 made of ZnO (zinc oxide) and a first transparent electrode made of Ta ₂ O ₅ are sequentially formed on a glass substrate 11 of the EL element 100 of FIG. After forming the insulating layer 13, a light emitting layer 14 made of TiZr ₂ S ₄ (zirconium titanium sulfide) to which Mn is added as a light emitting center is formed. Thereafter, the formation of the second insulating layer 15 and the second transparent electrode 16 is the same as in the first embodiment.
[0020]
The light emitting layer 14 is maintained at a constant temperature of 50 to 300 ° C. of the glass substrate 11, introduces an Ar gas into a sputtering apparatus, and uses a TiZr ₂ S ₄ : Mn powder target or a sintered target to obtain a 200 W power supply. It was formed by sputtering with high frequency power. Here, the amount of Mn charged in the sputter target was adjusted so that the Mn concentration in the TiZr ₂ S ₄ light emitting layer was in the range of 0.1 to 1.0 at%. Thereafter, heat treatment was performed in a high-temperature atmosphere of 550 ° C. or more for 4 to 40 hours.
[0021]
From the X-ray diffraction data, it was confirmed from the X-ray diffraction data that the parent TiZr ₂ S ₄ of the light-emitting layer 14 formed by the above film formation method belonged to the cubic system, had a spinel structure, and had a lattice constant of 10.26 °. Was. In this base material, the element having a valence of +2 is Ti, around which four S (sulfur) are coordinated, and the bond length of Ti-S is ~ 2.22 °. This was confirmed by the EXAFS method. FIG. 4 shows a state in which four S (sulfur) are coordinated around Ti (indicated by element X). This bond distance is shorter than the Zn-S bond distance of 2.34 ° of the ZnS: Mn light emitting layer in which four S (sulfur) are similarly coordinated. Accordingly, the interaction between the crystal field formed by S (sulfur) and +2 valent Mn becomes stronger, the peak wavelength of the emission spectrum shifts to a longer wavelength side than 590 nm, and red EL emission having a peak at 〜650 nm is obtained. .
[0022]
Among the host material structure elements of the light-emitting layer 14, the element X having a valence of +2, describe the reason for limiting the XS bonding distance Oa Ru numerical range. First, a case where six S (sulfur) are coordinated around the element X will be described. Such base materials include MgS (magnesium sulfide), CaS, SrS, BaS (barium sulfide), and MgIn ₂ S ₄ shown in the first embodiment of the present invention. FIG. 5 shows the relationship between the peak wavelength of the emission spectrum and the XS bond distance when Mn was added to these. Assuming that the peak wavelength at which red light emission is obtained is from 620 nm to 700 nm, this figure shows that the XS bond distance of 2.56 ° to 2.75 ° is a desirable numerical range for exhibiting red light emission.
[0023]
Next, a case where four S (sulfur) are coordinated around the element X will be described. Such base materials include ZnS, MgY ₂ S ₄ shown in the second embodiment of the present invention, and TiZr ₂ S ₄ shown in the third embodiment of the present invention. FIG. 6 shows the relationship between the peak wavelength of the emission spectrum and the X-S bond length when Mn is added to these. Assuming that the peak wavelength at which red light emission is obtained is from 620 nm to 700 nm, it can be understood from this figure that the XS bond distance of 2.15 ° or more and 2.27 ° or less is a desirable numerical range for exhibiting red light emission.
[0024]
As described above, a red light-emitting EL element that does not require a filter can be obtained by the structure of the present invention.
[Brief description of the drawings]
FIG. 1 is a view showing a longitudinal section of an EL element of the present invention.
FIG. 2 is a schematic view showing a state in which an element X is coordinated to S (sulfur) in a light emitting layer base material according to a first embodiment of the present invention.
FIG. 3 is a diagram showing an emission spectrum of the EL device according to the first embodiment of the present invention.
FIG. 4 is a schematic view showing a state in which an element X is coordinated to S (sulfur) in a light emitting layer base material according to a third embodiment of the present invention.
FIG. 5 is a diagram illustrating a relationship between an XS bond distance and an emission spectrum peak wavelength when six S (sulfur) are coordinated around an element X.
FIG. 6 is a diagram showing the relationship between the XS bond distance and the emission spectrum peak wavelength when four S (sulfur) are coordinated around the element X.
FIG. 7 is a schematic view showing a vertical cross section of an EL element.
[Explanation of symbols]
10, 100 EL element (electroluminescence element)
1,11 glass substrate (insulating substrate)
2, 12 First transparent electrode (first electrode)
3, 13 First insulating layer 4, 14 Light emitting layer 5, 15 Second insulating layer 6, 16 Second transparent electrode (second electrode)

Claims (2)

In the electroluminescent element in which the first electrode, the first insulating layer, the light emitting layer, the second insulating layer and the second electrode are sequentially laminated on at least the material on the light extraction side in an optically transparent manner,
The light emitting layer is a sulfur compound to which Mn (manganese) is added as an activator, and a crystal system of the sulfur compound belongs to one of an orthorhombic system and a cubic system,
Among the constituent elements of a sulfur compound, +2 coordinated six S (sulfur) around the element X with valence, Ri 2.75Å der less bond distance is more than 2.56Å for X-S,
Electroluminescent element sulfur compound is characterized <br/> be MgIn ₂ S ₄ (indium sulfide magnesium). In the electroluminescent element in which the first electrode, the first insulating layer, the light emitting layer, the second insulating layer and the second electrode are sequentially laminated on at least the material on the light extraction side in an optically transparent manner,
The light emitting layer is a sulfur compound to which Mn (manganese) is added as an activator, and a crystal system of the sulfur compound belongs to one of an orthorhombic system and a cubic system,
Among the constituent elements of the sulfur compound, four S (sulfur) coordinates around the element X having a valence of +2, and the bond distance of X-S is 2.15 ° or more and 2.27 ° or less ;
An electroluminescent device, wherein the sulfur compound is MgY ₂ S ₄ (yttrium magnesium sulfide ) or TiZr ₂ S ₄ ( zirconium titanium sulfide ) .

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