JP2005353578A - Light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EL element simultaneously reconciled in high luminance and low price. <P>SOLUTION: In the light emitting element having a first electrode, a dielectric layer, an emitter layer and a second electrode layered sequentially on a substrate, the dielectric layer is formed of a dielectric composed of a crystalline material with perovskite structure where the lattice constant of a c-axis is greater than the lattice constant of an a-axis obtained by X-ray diffraction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light emitting element that emits light by applying a voltage to an inorganic light emitter, and a display device using the light emitting element.

  A light-emitting element using an inorganic phosphor such as zinc sulfide as a light-emitting body (hereinafter referred to as an EL element) has spontaneous emission, excellent visibility, a wide viewing angle, and a high response speed. Application to display devices such as displays for computers and displays for personal computers is expected. Against this background, various proposals have been made with the aim of putting EL elements having high emission luminance and low cost into practical use.

  An EL element having a configuration in which a first electrode, a light emitting layer composed of a dielectric layer and an inorganic light emitting layer, and a second electrode are sequentially laminated on a substrate is generally well known. This type of EL element has higher emission luminance in proportion to the voltage applied to the light emitter layer. Therefore, in order to increase the emission luminance by increasing the applied voltage, the dielectric strength characteristics of the dielectric layer are important as described below.

When the light emission driving voltage Va is applied between the first electrode and the second electrode, the voltage Vp applied to the light emitter layer and the voltage Vi applied to the dielectric layer are expressed by the following formula (1). Is known (see, for example, Non-Patent Document 1).
Vp = εi · dp / (εidp + εpdi) · Va (1)
Vi = εp · di / (εpdi + εidp) · Va
Where εi is the relative dielectric constant of the dielectric layer, εp is the relative dielectric constant of the phosphor layer, di is the thickness of the dielectric layer, and dp is the layer thickness of the phosphor layer.

  As can be seen from the above equation (1), in order to increase the voltage Vp applied to the light emitting layer and increase the light emission luminance, the dielectric constant εi of the dielectric layer is increased and the layer thickness di is decreased. At the same time, the dielectric breakdown voltage of the dielectric layer needs to be equal to or higher than the voltage Vi. Realizing both the thinning of the dielectric layer and the high withstand voltage is an important technical problem required of the dielectric layer for high luminance.

  In order to solve this problem, many proposals for forming a dielectric layer by a thin film forming method such as a sputtering method have been made. However, the dielectric layer formed by the thin film formation method has a low dielectric strength because the denseness (hereinafter referred to as density) of the dielectric crystal is small (see, for example, Patent Document 1). Therefore, when a high voltage is applied to the light emitting layer, the dielectric layer breaks down, so that the light emission luminance cannot be increased. In view of this, Japanese Patent Application Laid-Open No. 2001-196184 proposes forming the dielectric layer by a thick film method in order to increase the density of the dielectric layer and increase the withstand voltage.

That is, a dielectric paste in which Ba ₂ AgNbO ₁₅ powder is dispersed in a binder resin is screen-printed on an alumina substrate and then baked at 1100 ° C. to form a high-density dielectric layer. At this time, unevenness of 1 μm or more is generated on the surface of the dielectric layer. When a light emitting layer is laminated on a dielectric layer with unevenness of 1 μm or more, the light emitting layer causes dielectric breakdown when a light emission driving voltage is applied. Therefore, the surface of the dielectric layer is polished to reduce the surface unevenness. It is necessary to planarize to 1 μm or less. The above configuration is used to increase the brightness.

Tatsuo Uchida and Hiraki Uchiike “Flat Panel Display Dictionary”, published by Industrial Research Council, December 25, 2001, page 386 JP 2001-196184 A

  However, since the conventional EL element disclosed in Japanese Patent Laid-Open No. 2001-196184 uses a dielectric fired at 1100 ° C., a special substrate having a high heat resistance temperature must be used. For this reason, there existed a problem that material cost became high. Further, a step of flattening the surface of the dielectric layer after firing is required. Therefore, there is a problem that the manufacturing cost increases because the number of man-hours increases.

  Therefore, an object of the present invention is to provide an EL element that solves the conventional problems and realizes high luminance and low price at the same time, and a display device using the EL element.

An EL device according to the present invention is a light emitting device having a light emitting layer in which a light emitting layer and a dielectric layer are laminated, and a pair of electrodes for applying an electric field to the light emitting layer,
The dielectric layer is composed of a dielectric made of a crystal having a perovskite structure, and the crystal has a c-axis lattice constant larger than an a-axis lattice constant determined by an X-ray diffraction method. . As a result, high brightness and low price were solved at the same time.

Moreover, the display device of the present invention includes:
A light emitting device in which a stripe-shaped first electrode, a dielectric layer, a light-emitting layer, and a stripe-shaped second electrode orthogonal to the first electrode are sequentially stacked on a substrate;
A simple matrix type display device having a drive circuit that applies a drive voltage between the first and second electrodes to cause the light emitting layer to emit light,
The dielectric layer is made of a dielectric made of a crystal having a perovskite structure, and has a c-axis lattice constant larger than an a-axis lattice constant obtained by an X-ray diffraction method of the crystal. . As a result, high brightness and low price were solved at the same time.

  According to the EL element and the display device of the present invention, the dielectric breakdown voltage of the dielectric layer is high, so that the emission luminance is high, and a versatile and inexpensive glass substrate can be used, so that the price can be reduced. Therefore, it is possible to obtain an effect of simultaneously realizing high brightness and low price applicable to a display such as a television.

  Embodiments of the present invention will be described with reference to the accompanying drawings. Note that substantially the same members are denoted by the same reference numerals.

(Embodiment 1)
FIG. 1 is a cross-sectional view schematically showing a cross section of an EL element according to Embodiment 1 of the present invention. The EL element 16 includes a striped back electrode 12 as a first electrode on a substrate 11, a dielectric layer 13 in which a dielectric is formed by a thin film forming method, and a light emitter layer 14 made of an inorganic light emitter. And a striped transparent front electrode 15 as a second electrode are sequentially laminated. The back electrode 12 and the front electrode 15 are arranged such that the extending directions of the respective stripes are orthogonal to each other. When a voltage is applied between the back electrode 12 and the front electrode 15, light 17 emitted from the light emitter layer 12 at the intersection of the back electrode 12 and the front electrode 15 is transmitted through the front electrode 15 and emitted.

Hereinafter, each component of the EL element 16 will be described.
As the substrate 11, any substrate that is used in a normal EL element, such as a ceramic substrate, a high heat-resistant plastic substrate subjected to heat treatment, and a glass substrate, can be applied. In particular, a glass substrate such as non-alkali glass is preferable because it has high mechanical strength and low material costs.

  As the back electrode 12, any conductor such as Pt, Pd, Au, Ir, Rh, Ni, etc. can be applied. If necessary, a laminate of these conductors or a mixture of these conductors may be used. Moreover, you may use the transparent conductor described below according to the objective.

As the front electrode 15, any generally known light-transmitting transparent conductor such as ITO (In ₂ O ₃ doped with SnO ₂ ), InZnO, or tin oxide can be applied. In addition, what is necessary is just to replace the electrode material demonstrated with the back electrode 12 and the front electrode 15 when taking out light from the board | substrate 11 side.

As the dielectric constituting the dielectric layer 13, any crystalline dielectric having a perovskite structure represented by ABO ₃ as shown in FIG. 2 can be applied. In particular, barium titanate (BaTiO ₃ ), barium strontium titanate ((Ba, Sr) TiO ₃ ), bismuth titanate (BiTiO ₃ , Bi: Ti = 4: 3), strontium titanate (SrTiO ₃ ), titanium bismuth lanthanum _{((Bi, La) TiO 3} , where Bi: La: Ti = 3.35: 0.75: 3) dielectric properties, dielectric strength characteristics, preferable from the viewpoint of excellent like the film formation characteristics. In addition, those in which any one of Ca, Mg, Bi, and Zr is doped with these dielectrics in an amount of 2 to 20 atomic% are preferable in that the variation of the emission luminance with respect to the environmental temperature change becomes small. FIG. 3 is a diagram showing the relationship between the ambient temperature and the light emission luminance of an EL element using a dielectric material in which BaTiO ₃ is doped with about 5 atomic% of Ca, Mg, Bi, and Zr. As is clear from this figure, all of the doped dielectrics have a smaller variation in light emission luminance with respect to environmental temperature changes compared to undoped BaTiO ₃ .

The dielectric layer 13 is preferably formed by a thin film forming method such as sputtering, CVD (chemical vapor deposition), or MOCVD (metal organic chemical vapor deposition). There are three reasons for this.
B) Since the density of the dielectric layer 13 is increased, the dielectric strength characteristics and the dielectric characteristics are improved.
B) Since a film can be formed at a low temperature of 600 ° C. or lower, it is possible to use an inexpensive glass substrate having a low heat-resistant temperature.
C) Since the surface roughness of the dielectric layer 13 is small and a layer having excellent flatness can be formed, the step of planarizing the surface of the dielectric layer 13 becomes unnecessary.

  The inventors have found through experiments that the dielectric characteristics and dielectric strength characteristics of the dielectric layer 13 have a large correlation with the microscopic crystal structure and crystal orientation of the dielectric forming the layer. Therefore, a preferred crystal structure and crystal orientation form of the dielectric layer 13 will be described below.

The crystal structure and crystal orientation were evaluated using an X-ray diffraction method. FIG. 4 is an example of a diffraction pattern obtained by measurement by the X-ray diffraction method. The peak position of the diffraction pattern appears corresponding to the spacing between the crystal faces of the dielectric crystal. From this diffraction pattern, the a-axis and c-axis lattice constants are obtained, and the ratio c / a (hereinafter referred to as c / a) of the c-axis lattice constant to the a-axis lattice constant is used as an evaluation index of the crystal structure. ₃ , (Ba, Sr) TiO ₃ , BiTiO ₃ , SrTiO ₃ , (Bi, La) TiO ₃ c / a and the correlation between the emission luminance was examined. As a result, the present inventors have found that a crystal structure in which the c-axis lattice constant is larger than the a-axis lattice constant is preferable. FIG. 5 shows the relationship between the lattice constant ratio c / a of the (Ba, Sr) TiO ₃ crystal and the light emission luminance. Referring to FIG. 5, when the lattice constant ratio c / a is greater than 1, light emission is obtained, and the light emission luminance suddenly increases from 1.004, and when it exceeds 1.006, the light emission luminance increases to 300 cd / m ² or more. I understand that Although other dielectrics were examined, similar results were obtained. In general, the backlight applications of the mobile phone 150 cd / ^{m 2} or more, the PC displays applications 300 cd / ^{m 2} or more, and as the TV use is said to require 500 cd / ^{m 2} or more light-emitting luminance Yes. Therefore, in the crystal structure of the dielectric layer 13, the lattice constant ratio c / a needs to be 1.004 or more in order to obtain a certain light emission luminance by starting to emit light. Further, in order to obtain an emission luminance of 150 cd / cm ² or more, the lattice constant ratio c / a is preferably 1.005 or more. Furthermore, in order to obtain an emission luminance of 300 cd / cm ² or more, the lattice constant ratio c / a is more preferably 1.006 or more.

Next, as shown in FIG. 6, the X-ray diffraction intensity Ia from the plane perpendicular to the a-axis, ie, (200) plane, and the X-ray diffraction intensity Ic from the plane perpendicular to the c-axis, ie, (002) plane, The correlation between Ic / Ia and emission luminance was examined using the ratio of the above (hereinafter referred to as Ic / Ia) as an evaluation index of crystal orientation. As a result, it has been found that it is preferable that the c-axis be oriented perpendicularly to the dielectric layer surface substantially parallel to the substrate surface in that the dielectric constant increases. As an example, FIG. 7 shows the relationship between the diffraction intensity ratio Ic / Ia of (Ba, Sr) TiO ₃ and the light emission luminance. Here, the chemical formula (Ba, Sr) TiO ₃ means a solid solution of BaTiO ₃ and SrTiO ₃ . Specifically, it is (Ba _1-x Sr _x ) TiO ₃ .

From FIG. 7, it can be seen that the emission luminance increases rapidly from the X-ray diffraction intensity ratio Ic / Ia = 0.4. Although other dielectrics were examined, similar results were obtained. Therefore, the crystal orientation of the dielectric constituting the dielectric layer 13 is such that the c-axis is oriented perpendicular to the dielectric layer surface substantially parallel to the substrate surface, and the X-ray diffraction intensity ratio Ic / Ia is 0.4 or more. Is preferable. In the case of BaTiO ₃ which is a representative material of the perovskite structure, the X-ray diffraction intensity Ic from the (002) plane of the crystal is 12.0 in the data by the powder diffraction method of the bulk material, and the (200) plane X-ray diffraction intensity Ia is 37.0, and the intensity ratio is Ic / Ia = 0.32. Further, (Ba _0.77 Sr _0.23 TiO ₃ is Ic / Ia = 0.07, and Ba _0.5 Sr _0.5 TiO ₃ is cubic in the bulk, so c = a, 2 Since the X-ray diffraction peaks of the two surfaces overlap, Ic / Ia is 1.

  The crystal constant lattice constant ratio c / a and the X-ray diffraction intensity ratio Ic / Ia described above are values measured by an “X-ray diffractometer” manufactured by Rigaku Corporation. The measurement conditions are shown below. X-rays were Cu-Kα rays. The X-ray output is 60 kV, 40 mA, the X-ray scan speed is 0.2 ° / min, the detection parallel slit and diverging slit width is 1 °, and the light receiving slit width is 0.30 mm. When calculating the X-ray diffraction intensity ratio, the diffraction intensity ratio obtained by subtracting the base line from the intensity of each diffraction peak is obtained.

FIG. 8 shows the experimental results of examining the correlation between the thickness of the dielectric layer 13 and the light emission luminance. From FIG. 8, it was found that when the layer thickness of the dielectric layer 13 is 1 μm or more, the emission luminance increases rapidly, and when the thickness is greater than 9 μm, the emission luminance decreases. This is because if the thickness is less than 1 μm, the withstand voltage is lowered, and a sufficient voltage cannot be applied to the dielectric layer 13, so that the light emission luminance is lowered. On the other hand, if it is thicker than 9 μm, the voltage applied to the light-emitting layer 14 is lowered, so that the light emission luminance is lowered. Therefore, the thickness of the dielectric layer 13 is preferably in the range of 1 to 9 μm in that high luminance of 300 cd / m ² or more can be obtained.

  In Table 1, Sample No. For the samples 1 to 19, the relationship between the thickness of the various dielectric layers 13 and the emission luminance was shown.

FIG. 9 shows the experimental results of investigating the relationship between the average surface roughness (hereinafter referred to as “surface roughness”) of the dielectric layer 13 adjacent to the light emitting layer 14 and the light emission luminance. As shown in FIG. 9, when the surface roughness is reduced to 0.4 μm or less, the emission luminance increases. When the surface roughness is about 0.3 μm, the emission luminance is 300 cd / m ² , and when the surface roughness is 0.2 μm, the emission luminance is 500 cd. / M ² is obtained, but it can be seen that the emission luminance is almost constant at a surface roughness of less than that. On the other hand, if the surface roughness is larger than 0.4 μm, almost no emission luminance can be obtained. This is because if the surface roughness of the dielectric layer 13 is large, the dielectric breakdown voltage of the light-emitting layer 14 is lowered and dielectric breakdown occurs, so that a high voltage cannot be applied. Accordingly, the surface roughness is preferably 0.3 μm or less in order to make the light emission luminance 300 cd / m ² or more. Moreover, in order to make the light emission luminance 500 cd / m ² or more, 0.2 μm or less is preferable.

  The surface roughness and the like of the dielectric layer were measured using a stylus type surface roughness meter (for example, Dektak (manufactured by Nippon Vacuum)). Further, the thickness of less than 0.1 μm, such as the nucleation layer and the buffer layer, was measured by a cross-sectional SEM and a cross-sectional TEM. Furthermore, the layer thickness in the range of 0.1 μm to 0.5 μm of each layer of the EL element can also be measured using the stylus type surface roughness meter.

  Further, the present inventor has found that when the vicinity of the surface of the dielectric layer 13 is made amorphous, the variation in surface roughness becomes smaller and the reliability is remarkably improved. As a method of making the surface layer portion of the dielectric layer 13 amorphous, there is a method of reverse sputtering after forming the dielectric layer 13 or a method of applying a high frequency bias to the substrate 11 again at the final stage of film formation. is there. The confirmation of the amorphized surface layer part can be performed as follows. For example, a section perpendicular to the depth direction of the surface is irradiated with an electron beam only on the surface layer portion with an analytical electron microscope, and a halo is obtained instead of a spot. I can confirm.

Next, a manufacturing method for forming the dielectric layer 13 by sputtering will be described.
A high-frequency bias is applied to the substrate 11 at the initial stage of film formation to seed a seed crystal of a dielectric crystal, that is, a crystal nucleus, on the substrate 11, and then the high-frequency bias is turned off to obtain a desired layer thickness. Form a film. When the film is formed after nucleation in this way, a dielectric crystal 13 is easily grown, so that a good dielectric layer 13 having a high density and a surface roughness of 0.3 μm or less can be obtained. If nucleation is repeated not only in the initial stage but also in the middle of film formation, a layer having a more uniform density can be obtained. In particular, it is extremely effective when applied when the layer thickness is increased.

  Table 2 shows Sample No. It is the experimental result which investigated about the sample to 20-31 about the relationship between the film thickness of a seed crystal | crystallization layer (seed crystal layer), and light-emitting luminance. From this table, it can be seen that both the forming seed crystal and the emission luminance are higher than those without nucleation. This is because nucleation increases the density of the dielectric layer 13 and increases the withstand voltage. It is not preferable that the nucleation film layer is thinner than 1 nm because the nucleation effect is small and the luminance is low. On the other hand, if the thickness is greater than 100 nm, the internal stress of the film increases and the dielectric layer 13 peels off from the substrate 11, which is not preferable. Therefore, the thickness of the nucleation is preferably in the range of 1 nm to 100 nm.

When the dielectric layer 13 is formed by CVD or MOCVD, BaTiO ₃ , (Ba, Sr) TiO ₃ , BiTiO ₃ , SrTiO ₃ , (Bi, La) TiO ₃ are formed using the following raw materials. . Nucleation can be performed by sputtering.

Examples of the raw material for the dielectric layer include the following. That is, Ti (OiC ₃ H ₇ ) ₄ , Ba (OCH ₃ ) ₂ , Ta (OiC ₂ H ₅ ) ₅ , Sr (OCH ₃ ) ₂ , La (OiC ₃ H ₇ ) ₃ , Zr (OiC ₃ H ₇ ) ₄ or alcohol (Ba (METHD) ₂ , Ba (THD) ₂ , Sr (METHD) ₂ , Sr (THD) ₂ , Ti (MPD) (THD) ₂ , Ti (MPD) (METHD) ₂ , Ti ( THD) ₂ (OiPr) ₂ , BiPh ₃ , Bi (MMP) ₃ , Bi (Ot-Am) ₃ , La (EDMDD) ₃ , Pb (METHD) ₂ , Pb (THD) ₂ , Zr (METHD) ₄ , Zr (THD) ₂ , Zr (MTHD) ₄ , Zr (Ot-Bu) ₄ , Zr (MMP) ₄ , 2-ethylhexanoic acid Zr, Ti, Ba, Sr, or the like is used. Here, METHD is 1- (2-) 2,2,6,6-tetramethyl-3,5-heptanedionate, MTHD is 1-methoxy-2,2,6,6-tetramethyl-3,5-heptanedionate , THD is 2,2,6,6-tetramethyl-3,5-heptaneconate, MPD is 2-methyl-2,4-pentanedioxide, MMP is 1-methoxy-2-methyl-2-propoxide, EMDDD Is 6-ethyl-2,2-dimethyl-3,5-decanedionato, OD is 2,4-octandionato, ND is 2,4-nonandionato, Ti (THD) ₂ (OiPr) ₂ is Ti (THD) ₂ (OiC ₃ H ₇ ) ₂ , BiPh ₃ is triphenylbismuth, Bi (Ot—Am) ₃ is Bi (OtC ₅ H ₁₁ ) ₃ , Zr (Ot—Bu) ₄ is Zr (OtC ₄ H ₉ ) ₄ is there.

  When the dielectric layer 13 described above is used for an EL element, it is possible to apply a high voltage to the light emitting layer 14, which is preferable in terms of increasing the light emission luminance. Further, the light emitter layer 14 can be formed directly on the dielectric layer 13. Therefore, a planarization step such as polishing the surface of the dielectric layer is not necessary, which is preferable in that the manufacturing cost is reduced.

FIG. 15 is an oxygen concentration profile in the film thickness direction of the dielectric layer 13 in the present invention. The amount of oxygen in the film from the film surface to the substrate in the case of (Ba, Sr) TiO ₃ as the dielectric layer is represented. The oxygen amount was evaluated by Auger spectroscopy. However, the oxygen amount evaluation method is not limited to this, and any method can be used as long as the oxygen amount is measured while etching from the film surface. Referring to FIG. 15, it can be seen that the dielectric layer of the present invention has a larger amount of oxygen at the substrate interface than the comparative example. This seems to be due to the increased amount of oxygen taken in due to nucleation. Here, the comparative example is a dielectric layer formed under the same conditions without nucleation. Also, the amount of oxygen in the dielectric film of the present invention was larger than in the comparative example. When In is the oxygen concentration at the substrate boundary when nucleation is performed in this embodiment and Io is the oxygen concentration at the substrate boundary when nucleation is not performed, high luminance is obtained by setting In / Io ≧ 1.1. A film having a high withstand voltage can be obtained. As for the oxygen concentration in the film, if the oxygen concentration in the film when nucleation is performed in this embodiment is Ibn and the oxygen concentration in the film without nucleation is Ibo, Ibn / Ibo ≧ 1 .05 can provide a film with high luminance and high withstand voltage. Therefore, this amount of oxygen also affects the crystallinity and can be a factor for obtaining high brightness and high withstand voltage.

Examples of the light emitter applicable to the present invention include sulfides such as ZnS: Mn, Cu, SrS, BaAl ₂ S ₄ , and CaS, or transitions such as Mn and Cr in oxides such as ZnO, Y ₂ O ₃ , and ZnSiO _4. Any generally known material such as a metal or a material added with an emission center such as a rare earth metal such as Eu or Ce can be applied. An example of a specific light emitter is shown below.

Blue light emitters include SrS: Cu, SrS: Cu, Ag, ZnS: Tm, BaAlS ₄ : Eu, CaGa ₂ S ₄ : Ce, and the like. Examples of blue-green light emitters include ZnS: Cu, SrS: Ce, and the like. Examples of the green light emitter include ZnS: Tb, F, ZnS: Tb, ZnS: TbOF. In addition, red light emitters include CaS: Eu, CaSSe: Eu, and ZnS: Mn. Moreover, as a white light-emitting body, there exists what laminated | stacked the blue, green, and red light-emitting body mentioned above.

(Embodiment 2)
FIG. 10 is a cross-sectional configuration diagram schematically showing a cross section of another EL element 102 according to the present invention. The configuration is the same as that described in FIG. 1 except that the buffer layer 101 is provided between the back electrode 12 and the dielectric layer 13. In addition, the same code | symbol was provided to the same thing as the component demonstrated in FIG.

As the buffer layer 101, a composition expressed by a chemical formula Mg _x Si _1-x O _2-x (0.9 ≦ x ≦ 1) is used. When the dielectric layer 13 is formed on the buffer layer 101 made of this composition, the crystallinity and crystal orientation of the dielectric are improved. A composition outside this range is unsuitable because the crystal structure of the face-centered cubic (fcc) or NaCl type, which is the basic structure of MgO, is disturbed and the crystal orientation deteriorates.

Table 3 shows Sample No. It is the experimental result which investigated the relationship between the layer thickness of the buffer layer 101, and light-emitting luminance about the sample to 32-51. The layer thickness of the buffer layer 101 is preferably in the range of 1 nm to 100 nm. When the thickness of the buffer layer is less than 1 nm, the light emission luminance is low because the effect of promoting crystal growth is small. On the other hand, when it is thicker than 100 nm, the light emission luminance is lowered. Therefore, when the thickness of the buffer layer 101 is in the range of 1 nm to 100 nm, high luminance of 300 cd / m ² or more can be obtained. The buffer layer 101 can be formed by a normal thin film forming method such as a sputtering method.

(Embodiment 3)
FIG. 11 is a cross-sectional view schematically showing a cross section of the EL element 112 according to Embodiment 3 of the present invention. Compared with the EL elements of the first and second embodiments, this EL element is provided between the back electrode 12 made of a conductor containing any of Pt, Pd, Au, Ir, Rh, and Ni and the glass substrate 11. The configuration is the same as that described in FIG. 1 or 10 except that the formation 111 is different.

  The underlayer 111 is composed of a layer having a thickness of 5 to 50 nm including any of Ti, Co, and Ni. By providing the base layer 111, the adhesion between the glass substrate 11 and the back electrode 12 is improved.

(Embodiment 4)
FIG. 12 is a perspective view schematically showing a main part of a display device using an EL element according to Embodiment 4 of the present invention. The display device 121 is based on a simple matrix driving method, and the EL elements 122 described in the first to third embodiments are arranged in a two-dimensional matrix, and includes a data signal driving circuit 123 and an operation signal driving circuit. 124. The stripe-shaped back electrode 12 is connected to the operation signal drive circuit 124, and the stripe-shaped front electrode 15 orthogonal to the back electrode 12 is connected to the data drive circuit 123. The data signal voltage output from the data signal drive circuit 123 and the operation signal voltage output from the operation signal drive circuit 124 are applied to the portion where the back electrode 12 and the front electrode 15 intersect to make the EL element 122 Make it emit light.

As shown in FIG. 13, by using an EL element in which a color conversion layer 131 is provided on the front electrode 15, a display device that displays colors from green to red can be obtained. Further, by using an EL element that emits white light and providing red, blue, and green color filters 141 on the front electrode 15 as shown in FIG. 14, a display device that displays full color can be obtained.
With the above-described configuration, it is possible to simultaneously realize high brightness applicable to a display such as a television and low price of the device.

  Next, a more detailed description will be given based on specific examples.

(Example 1)
An EL device according to Example 1 of the present invention will be described. This EL element has the configuration shown in FIG. This EL element 16 was produced by the manufacturing method described below.
(A) As the substrate 11, a commercially available non-alkali glass substrate (hereinafter referred to as a glass substrate) having a 1-inch square and a thickness of 0.635 mm was used.
(B) Next, a Ta layer and a Pt layer were laminated on the glass substrate 11 in this order by the sputtering method to form the back electrode 12. The layer thickness of the Ta layer as the underlayer was 30 nm, and the layer thickness of the Pt layer was 200 nm.
(C) Next, dielectric (Ba, Sr) TiO ₃ was used as a sputtering target, and after sputtering for 100 seconds while applying a high frequency bias to the glass substrate 11 (forming seed crystal), the high frequency bias was stopped. Then, a dielectric layer was formed by sputtering for another 60 minutes.
(D) Then, the surface of the dielectric layer was made amorphous by sputtering for 100 seconds while applying a high frequency bias to the glass substrate 11 again. As a result, a dielectric layer 13 having a layer thickness of 3 μm was formed on the back electrode 12.

  The sputtering conditions for forming the dielectric layer are shown below. As the sputtering gas, a mixed gas having a gas flow ratio of 0.5 oxygen gas to argon gas 25 was used. The sputtering pressure was about 1.6 Pa (12 mTorr). The sputter power at the time of nucleation was 500 W, and the sputter power at the time of film formation was 2 kW. The high frequency bias was 300 W and the substrate temperature was 500 ° C.

As a result, a dielectric layer 13 having a seed crystal layer thickness of about 10 nm, a relative dielectric constant of 510, a withstand voltage of 3 × 10 ⁶ V / cm, and an average surface roughness of 0.08 μm is obtained. It was.

The ratio c / a of the crystal constants of the crystal constituting the dielectric layer is 1,007, and the X-ray diffraction intensity ratio Ic / Ia between the (002) plane and the (200) plane of the crystal is 0. 0. 7.
(E) Next, using SrS: Ce (the amount of Ce added is about 1.5 mol%) as a sputtering target, sputtering is performed on the dielectric layer 13 by a high-frequency magnetron sputtering method, and a thickness of about 500 nm is obtained. The phosphor layer 14 was formed. At this time, the sputtering gas was argon gas, the sputtering pressure was 0.53 Pa (4 mTorr), and the glass substrate temperature was 300 ° C.
(F) Next, an ITO film was sputtered on the phosphor layer 14 by a sputtering method to form a front electrode 15 made of the ITO film, thereby creating an EL element 16.
When the EL device 16 manufactured as described above was applied with an AC voltage of 200 V, 1 kHz and a pulse width of 50 μs to measure the light emission luminance, a light emission luminance of 500 cd / m ² was obtained. In addition, dielectric breakdown did not occur even when a voltage of 300 V was applied.

(Example 2)
An EL light emitting device having the configuration shown in FIG. 10 was produced by the manufacturing method described below. The components other than the buffer layer 101 were created by the same method as in Example 1.
The buffer layer 101 was formed by sputtering a composition of the chemical formula Mg _0.98 Si _0.02 O _{1.02 on} the back electrode 12 by sputtering. As a result, when the emission luminance was measured by applying an AC voltage of 200 V, 1 kHz and a pulse width of 50 μsec to the EL element 16 manufactured as described above, the emission luminance was 524 cd / m ² .

  Since the light-emitting element according to the present invention has high emission luminance and can be manufactured at low cost, surface light emission of a display device mounted on a digital camera, a mobile phone, a portable information terminal, a personal computer, a TV, an automobile, and the like and a backlight of a liquid crystal display Applicable to source.

  As described above, the present invention has been described in detail with reference to the preferred embodiments. However, the present invention is not limited thereto, and many preferred embodiments are within the technical scope of the present invention described in the claims. It will be apparent to those skilled in the art that variations and modifications are possible.

It is sectional drawing of the EL element which concerns on this invention. It is the schematic diagram which showed the crystal structure of the dielectric material used for this invention. It is the figure which showed the relationship between the environmental temperature of an EL element, and a brightness | luminance. It is the measurement data of FIG. 3A. 3 is an X-ray diffraction chart in a partial angle range of a dielectric layer. It is the figure which showed the relationship between the lattice constant ratio c / a of the dielectric crystal which comprises a dielectric material layer, and light emission luminance, It is the measurement data of FIG. 5A. In the X-ray diffraction chart of a dielectric material layer, it is the schematic which shows the indexed surface and its diffraction intensity. It is the figure which showed the relationship between the X-ray-diffraction intensity ratio of the (002) plane of a dielectric crystal which comprises a dielectric material layer, and a (200) plane, and light emission luminance. It is the measurement data of FIG. 7A. It is a figure which shows the relationship between the layer thickness of a dielectric material layer, and light emission luminance. It is the measurement data of FIG. 8A. It is the figure which showed the relationship between the surface roughness of the dielectric material layer by this invention, and light emission luminance. It is the measurement data of FIG. 9A. It is sectional drawing of the EL element which concerns on Embodiment 2 of this invention. It is sectional drawing of the EL element which concerns on Embodiment 3 of this invention. It is the schematic which showed typically the principal part of the display apparatus which concerns on Embodiment 4 of this invention. It is sectional drawing of the display apparatus of another example which concerns on Embodiment 4 of this invention. It is sectional drawing of the display apparatus of the another example which concerns on Embodiment 4 of this invention. It is the oxygen concentration profile of the film thickness direction of the dielectric material layer of the EL element with a nucleation layer at the time of dielectric layer preparation, and the EL element without a nucleation layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Board | substrate, 12 Back electrode, 13 Dielectric layer, 14 Light emitter layer, 15 Front electrode, 16, 102, 112, 122 EL element, 17 Light, 101 Buffer layer, 111 Underlayer, 121 Display device, 123 Data signal drive Circuit, 124 operation signal drive circuit, 131 color conversion layer, 141 color filter

Claims (21)

A light emitting layer formed by laminating a light emitting layer and a dielectric layer;
A pair of electrodes for applying an electric field to the light emitting layer,
The light emitting element, wherein the dielectric layer is made of a dielectric made of a crystal having a perovskite structure, and the crystal has a larger c-axis lattice constant than an a-axis lattice constant.   2. The light-emitting element according to claim 1, wherein a lattice constant of the c-axis of the crystal body is 1.004 times or more of a lattice constant of the a-axis.   2. The light-emitting element according to claim 1, wherein a lattice constant of the c-axis of the crystal body is 1.006 times or more of a lattice constant of the a-axis.   4. The light emitting device according to claim 1, wherein the dielectric layer mainly includes a crystal body in which the c-axis is oriented perpendicularly to the surface of the dielectric layer. 5.   In the X-ray diffraction intensity at the surface of the dielectric layer, the maximum diffraction intensity from the plane perpendicular to the c-axis of the crystal is 0.4 times or more of the maximum diffraction intensity from the plane perpendicular to the a-axis. The light emitting device according to claim 1, wherein the light emitting device is provided.   The X-ray diffraction intensity on the surface of the dielectric layer is characterized in that the diffraction intensity from the (002) plane of the crystal is 0.4 times or more the diffraction intensity from the (200) plane. The light emitting device according to any one of 1 to 4.   The light emitting device according to claim 1, wherein an average surface roughness of a surface of the dielectric layer adjacent to the light emitting layer is 0.3 μm or less.   The light emitting device according to claim 1, wherein a surface layer portion of the dielectric layer adjacent to the light emitting layer is amorphized.   The light emitting device according to any one of claims 1 to 8, wherein the dielectric layer has a layer thickness in a range of 1 µm to 9 µm. A buffer layer containing an oxide represented by a chemical formula Mg _x Si _1-x O _2-x (where 0.9 ≦ x ≦ 1) is provided between the first electrode and the dielectric layer. The light emitting device according to claim 1, wherein the light emitting device is a light emitting device.   The light emitting device according to claim 10, wherein the buffer layer has a thickness in a range of 1 nm to 100 nm.   12. The dielectric layer according to claim 1, wherein the dielectric layer includes at least one dielectric selected from the group consisting of barium titanate, barium strontium titanate, bismuth titanate, strontium titanate, and bismuth lanthanum titanate. The light emitting element as described in any one.   The light emitting device according to claim 12, wherein the dielectric is doped with at least one element selected from the group consisting of Ca, Mg, Bi, and Zr.   The light emitting device according to claim 1, wherein the light emitting layer further includes a nucleation layer for forming the dielectric layer.   The light emitting device according to any one of claims 1 to 13, wherein the light emitting layer further includes a plurality of nucleation layers that are stacked during the formation of the dielectric layer. A substrate and an underlayer;
The back electrode of the pair of electrodes is formed on the substrate, the light emitting layer is formed on the back electrode, and the base layer is formed between the substrate and the back electrode. The light-emitting element according to claim 1, wherein the light-emitting element is a light-emitting element.   The light emitting device according to claim 16, wherein the underlayer is made of any one of Ti, Co, and Ni.   The light emitting device according to claim 17, wherein the back electrode is made of a conductor containing any one of Pt, Pd, Au, Ir, Rh, Ni, and Ag.   The light emitting device according to any one of claims 1 to 18, further comprising a color conversion layer formed on an upper electrode provided on the light emitting layer of the pair of electrodes. .   The light emitting device according to claim 19, further comprising a color filter layer formed to cover the color conversion layer. 21. The light emitting device according to claim 1, further comprising a glass substrate on which the light emitting layer and a pair of electrodes are formed.

Images