JP2007329172A - Light-emitting element, manufacturing method thereof, and light-emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-emitting element for radiating a mixed color light having a high yield and small variation in characteristics. <P>SOLUTION: A GaN-based light-emitting layer 3 is formed on an MGC 2 (melt growth composite) consisting of a Y<SB>3</SB>Al<SB>5</SB>O<SB>12</SB>single crystal phase 21 and an Al<SB>2</SB>O<SB>3</SB>single crystal phase 22, and Ce<SP>3+</SP>ions are doped in the Y<SB>3</SB>Al<SB>5</SB>O<SB>12</SB>single crystal phase 21. In this way, a blue light radiated from the light-emitting layer 3 is transmitted through the Al<SB>2</SB>O<SB>3</SB>single crystal phase 22, passes through the Y<SB>3</SB>Al<SB>5</SB>O<SB>12</SB>single crystal phase 21, and excites the Ce<SP>3+</SP>ions to radiate a yellow light. The blue and yellow lights are mixed, thereby obtaining a white light. Also, the characteristics of the light-emitting element can be controlled by adjusting the thickness of the MGC 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technology of a light emitting device that emits white light by mixing two colors of light.

  In recent years, light emitting diodes have been used as illumination. Since white light is optimal for illumination, research and development of white light-emitting diodes has been actively conducted. As light-emitting diodes used for illumination, those described in Patent Document 1 and Patent Document 2 are known.

  As shown in FIG. 7A, a conventional white light emitting diode has a structure in which a light emitting element 71 that emits blue light is surrounded by a resin 72 containing a phosphor. The phosphor is excited by the blue light emitted from the light emitting element 71 to emit yellow light. As a result, a white light emitting diode that emits white light by mixing blue light and yellow light is obtained. Note that light emitting diodes of various light emitting colors can be manufactured by changing the light emitting color of the light emitting element 71 and the light emitting color of the phosphor contained in the resin 72. Further, as shown in FIG. 7B, it is also known that the light emitting element 71 is surrounded by a resin 72 containing a phosphor and covered with a transparent resin mold 73.

On the other hand, in the field of high-temperature structural materials, MGC (Melt Growth Composite) is known as a material excellent in bending strength, thermal stability, and creep resistance (Patent Document 3, non-patent document). Reference 1 and Non-Patent Document 2). For example, the MGC has an amorphous layer formed at the boundary portion formed by continuously and three-dimensionally intertwining a single crystal of Al ₂ O _{3 and} a single crystal of Y ₃ Al ₅ O ₁₂ while maintaining the single crystal. There is no ceramic composite material.

If Ce ³⁺ ions are doped into a single crystal of MGC Y ₃ Al ₅ O ₁₂ , it can be used as a light conversion element. For example, as shown in FIG. 8, is irradiated with blue light of the blue light emitting diode 83 to MGC80 processed into a plate shape, although it transmitted the blue light 84 is in the Al ₂ O ₃ single crystal 82 of MGC80, MGC80 of Y _The light that has passed through the ₃ Al ₅ O ₁₂ single crystal 81 excites Ce ³⁺ ions to emit yellow light 85. In addition, the refractive indexes of each crystal are 1.76 for Al ₂ O _{3 and} 1.82 for Y ₃ Al ₅ O ₁₂ , which are slightly different, and each crystal is connected continuously and three-dimensionally. Therefore, since the blue light 84 and the yellow light 85 are scattered and diffused in the MGC 80 while being mixed, a more uniform and efficient white light 86 can be obtained. In addition, the thing of patent document 4 is known as a light emitting diode using MGC as a light conversion element.
Japanese Patent No. 3724490 Japanese Patent No. 3724498 Japanese Patent No. 3216683 JP 200649410 A Nature, Vol. 389, No. 6646, p.49-52 Journal of the Europian Ceramic Society, 25 (2005), p.1441-1445

  However, in the conventional structure in which the phosphor 72-containing resin 72 is coated around the light emitting element 71 as shown in FIG. 7, the phosphor concentration increases or the resin 72 increases in thickness. Since the absorption by the body increases and the blue transmitted light decreases, the mixed color becomes yellow. For this reason, the light emission intensity, chromaticity, and spatial distribution of the light emitting diode change sensitively depending on the concentration of the light emitter and the state of resin potting, which causes wide variations in product characteristics and low yield.

  The present invention has been made in view of the above, and it is an object of the present invention to reduce a light emitting element that emits mixed color light with high yield, little variation in characteristics such as light emission intensity, chromaticity, and spatial distribution. To provide at a cost.

  The light-emitting device according to the first aspect of the present invention is formed by one and more single metal oxide single crystals and one or more composite metal oxide single crystals entangled with each other continuously and three-dimensionally. It has a ceramic composite in which at least one kind of metal oxide is doped with a light emitter, and a light emitting layer formed on the ceramic composite.

  In the present invention, a light emitting layer is provided on a ceramic composite formed by continuously and sterically intermingling one or more kinds of single metal oxides and one or more kinds of composite metal oxides. By doping the emitter with a light emitter, the light emitted from the light emitting layer excites the light emitter and emits light of another wavelength when passing through the metal oxide doped with the light emitter. It is possible to obtain mixed color light in which the emitted light and the light emitted by exciting the light emitter are mixed. In addition, compared to the case where the phosphor is included in the resin, the concentration of the phosphor that is doped in the metal oxide is more uniform in the entire region. Therefore, by adjusting the thickness of the ceramic composite, the emission intensity, color, The degree and spatial distribution can be controlled.

Here, it is desirable that the single metal oxide is Al ₂ O ₃ and the composite metal oxide is Y ₃ Al ₅ O ₁₂ in order to use the ceramic composite as the substrate of the light emitting element.

Further, it is preferable that the Al ₂ O ₃ single crystals are arranged in the <1-100> direction and the Al ₂ O ₃ crystal plane of the ceramic composite surface forming the light emitting layer is {0001}. It is desirable for growth.

In the light-emitting element, the light-emitting layer is a GaN-based light-emitting layer, and the light emitter is Ce ³⁺ .

In the present invention, the blue light emitted from the GaN-based light emitting layer excites Ce ³⁺ doped in the metal oxide to emit yellow light, thereby mixing the blue light and the yellow light. White light can be obtained.

  In addition, it is desirable that the average distance at which metal oxide single crystals appear periodically is 1 to 200 μm in order to grow the light emitting layer flatly.

  In the light-emitting element, the surface on which the light-emitting layer of the ceramic composite is formed has one or more kinds of metal oxides formed in a convex shape.

  In the present invention, the surface of the ceramic composite forming the light emitting layer is etched to make the metal oxide convex, so that the light emitting layer grows laterally from the convex metal oxide, so that the flat light emission A layer can be formed.

Moreover, it is desirable that the metal oxide formed in a convex shape is Al ₂ O ₃ in order to laterally grow a light-emitting layer with good crystallinity.

  Further, it is desirable that the height of the convex shape is higher than 1 μm and within 10 μm in order to form the light emitting layer flat.

  According to a second aspect of the present invention, there is provided a method for manufacturing a light emitting device, wherein one or more kinds of single metal oxides and one or more kinds of composite metal oxides are formed in a continuous and sterically entangled manner, And a step of epitaxially growing a light emitting layer on a wafer cut from a ceramic composite doped with a light emitter in at least one of the above, and a step of cutting a light emitting element from the wafer on which the light emitting layer is formed. Features.

  In the present invention, a light emitting element that emits mixed color light can be manufactured by growing a light emitting layer directly on a ceramic composite wafer by a process similar to the conventional method of manufacturing a light emitting element.

  The method for producing a light emitting device, further comprising the step of forming one or more kinds of metal oxides into a convex shape by etching one surface of a wafer cut out from the ceramic composite, and growing the light emitting layer Is characterized in that a light emitting layer is grown on the surface on which the convex shape is formed.

  A light emitting device according to a third aspect of the present invention is characterized in that the light emitting element according to the first aspect of the present invention is sealed with a transparent resin or glass.

  In the present invention, since the light emitting element is sealed with a transparent resin or glass, the color is sufficiently mixed in the transparent resin / glass, so that more uniform mixed color light can be obtained.

  In the above light emitting device, the light emitting element according to the first aspect of the present invention is flip-chip mounted with the light emitting layer facing downward.

  In the present invention, the light emitted from the light emitting layer is emitted through the upper ceramic composite by flip chip mounting the light emitting element, so that more uniform color mixing light can be obtained.

  Further, the refractive index of the transparent resin and the glass is preferably 1.4 to 1.8 in order to obtain a high light extraction efficiency by sufficiently mixing light.

  According to the present invention, it is possible to provide a light-emitting element that emits mixed color light at low cost with high yield, little variation in characteristics such as light emission intensity, chromaticity, and spatial distribution.

[First Embodiment]
FIG. 1 is a cross-sectional view illustrating the structure of the light-emitting element in this embodiment. As shown in the figure, the light-emitting element 1 is composed of an MGC 2 composed of a Y ₃ Al ₅ O ₁₂ single crystal phase 21 and an Al ₂ O ₃ single crystal phase 22 and a GaN-based light emitting layer 3 formed on the MGC 2. The The light emitting layer 3 emits blue light having a wavelength of 400 to 500 nm by passing an electric current. Further, the Y ₃ Al ₅ O ₁₂ single crystal phase 21 Ce ³⁺ ions are doped as an emitter.

Blue visible light emitted from the light emitting layer 3 is incident on the MGC 2. Since the transmittance of the Al ₂ O ₃ single crystal phase 22 is high, the average transmittance in the MGC 2 is 30% or more, and 30% or more of the incident blue visible light is transmitted as it is. The light passing through the Y ₃ Al ₅ O ₁₂ single crystal phase 21 excites Ce ³⁺ ions and emits yellow visible light. White light can be obtained by mixing the blue and yellow visible light.

As shown in FIG. 2, the MGC 2 has a shape in which the Al ₂ O ₃ single crystal phase 22 and the Y ₃ Al ₅ O ₁₂ single crystal phase 21 are intertwined uniformly and continuously in three dimensions. The size of each of these phases can be controlled by a solidification method, but when the light emitting layer 3 is epitaxially grown on the MGC ₂ , the Al ₂ O ₃ single crystal phase 22 and the Y ₃ Al ₅ O ₁₂ single crystal phase 21 appear periodically. The average distance (average periodic distance) is preferably 1 to 200 μm, particularly 1 to 50 μm.

The crystal plane Al ₂ O ₃ single crystal phase 22 of the surface of the MGC2 forming the light-emitting layer 3 is Miller index {0001}, the direction in which side by side Al ₂ O ₃ single crystal phase 22 <1-100 > Direction. Thereby, when the light emitting layer 3 is grown and formed on the MGC 2, the rate of lateral growth in the <11-20> direction of the light emitting layer 3 grown on the Al ₂ O ₃ single crystal phase 22 is increased. Since the Y ₃ Al ₅ O ₁₂ single crystal phase 21 is covered in a short time, the light emitting layer 3 can be formed satisfactorily.

When the average periodic distance 4 between the Al ₂ O ₃ single crystal phase 22 and the Y ₃ Al ₅ O ₁₂ single crystal phase 21 is increased, the light emitting layer 3 grows on the Y ₃ Al ₅ O ₁₂ single crystal phase 21. Since it is slower than the growth on the Al ₂ O ₃ single crystal phase 22, the surface of the light emitting layer 3 formed on the MGC 2 is uneven as shown in FIG. 3, and a mirror surface cannot be obtained. If sufficient time is taken, the surface of the light emitting layer 3 becomes flat even if the average periodic distance 4 is 100 μm or more, but it is a relatively short time within 10 hours by MOCVD (Metal Organic Chemical Vapor Deposition). In order to form the light emitting layer 3, the average periodic distance 4 is practically 50 μm or less.

FIG. 4 is a cross-sectional view showing the structure of MGC 2 obtained by etching the Y ₃ Al ₅ O ₁₂ single crystal phase 21. The MGC 2 shown in the figure is obtained by selectively etching the Y ₃ Al ₅ O ₁₂ single crystal phase 21 using a phosphoric acid-based etching solution, leaving the Al ₂ O ₃ single crystal phase 22 in a convex shape. . Since the light emitting layer 3 is laterally grown from the Al ₂ O ₃ single crystal phase 22 by epitaxially growing the GaN-based light emitting layer 3 on the etched surface, the light emitting layer 3 having a flat surface as shown in FIG. Can be obtained.

Note that the etching depth (convex height) of the Y ₃ Al ₅ O ₁₂ single crystal phase 21 is set to be deeper than 1 μm and within 10 μm. Although depending on the average periodic distance 4 of the MGC 2, if the etching depth is within 1 μm, the GaN crystal layer 5 grown on the Y ₃ Al ₅ O ₁₂ single crystal phase 21 at the bottom of the recess becomes the Al ₂ O ₃ single crystal phase 22. There is a risk of bonding to the laterally grown light emitting layer 3. When the average periodic distance 4 is 50 μm and the etching depth is 10 μm, the GaN crystal layer 5 grown on the Y ₃ Al ₅ O ₁₂ single crystal phase 21 is not bonded to the light emitting layer 3. Further, the dislocation density of the light emitting layer 3 is reduced by about one digit from the usual.

Therefore, according to the present embodiment, the GaN-based light emitting layer 3 is formed on the MGC 2 composed of the Y ₃ Al ₅ O ₁₂ single crystal phase 21 and the Al ₂ O ₃ single crystal phase 22 doped with Ce ³⁺ ions. By doing so, the blue light emitted from the light emitting layer 3 is transmitted through the Al ₂ O ₃ single crystal phase 22 and radiates yellow light by exciting Ce ³⁺ in the Y ₃ Al ₅ O ₁₂ single crystal phase 21. White light can be obtained by mixing blue light and yellow light. Further, since the concentration of Ce ³⁺ ions is substantially uniform in the entire region, the emission intensity, chromaticity, and spatial distribution can be controlled by adjusting the thickness of MGC2.

According to the present embodiment, by adjusting the average periodic distance 4 between the Al ₂ O ₃ single crystal phase 22 and the Y ₃ Al ₅ O ₁₂ single crystal phase 21, light emission having the light emitting layer 3 formed flat. An element can be obtained.

According to the present embodiment, the Y ₃ Al ₅ O ₁₂ single crystal phase 21 is etched, and the light emitting layer 3 is epitaxially grown on the surface where the Al ₂ O ₃ single crystal phase 22 is left in a convex shape, thereby forming a flat surface. A light emitting element having the light emitting layer 3 formed can be obtained.

  The MGC may contain two or more types of single metal oxides or two or more types of composite metal oxides. Other examples of the single metal oxide and the composite metal oxide constituting the MGC are described in Patent Document 4.

[Second Embodiment]
In the second embodiment, a manufacturing method for manufacturing a light emitting element in which a blue light emitting layer is formed on an MGC composed of an Al ₂ O ₃ single crystal and a Y ₃ Al ₅ O ₁₂ single crystal will be described.

Solidification direction is from <1-100> Al ₂ O ₃ in the direction monocrystalline phase and Y ₃ Al ₅ O ₁₂ single crystal phase, the average period length is 10μm MGC Al ₂ O ₃ single crystal phase from the <1-100 > A substrate with a {0001} plane orientation is cut out and mirror-polished to produce an MGC wafer having a diameter of 2 inches (about 5 cm) and a thickness of 0.35 mm.

  Subsequently, this MGC wafer is set on a susceptor of an MOCVD apparatus, and hydrogen is used as a carrier gas, TMG (trimethylgallium) and ammonia are used as source gases, and a two-step growth low temperature buffer layer is grown at 500 ° C. to 20 nm.

  Thereafter, the TMG is stopped, the temperature is raised to 1080 ° C., and then the TMG is flowed again to grow a non-doped GaN layer by 20 μm. Finally, a blue light emitting layer having a predetermined peak emission wavelength of 470 nm is formed on the MGC wafer. The MGC wafer on which the blue light emitting layer is formed is processed into chips by a normal process.

  As described above, by using the MGC wafer as the substrate of the blue light emitting layer, a white light emitting element can be manufactured in the same process as that for manufacturing a normal blue light emitting element.

In addition, in epitaxial growth between different types of crystals having different lattice constants and crystal systems, crystals grow so that strain energy and surface energy are stabilized. Therefore, when the light emitting layer 3 is epitaxially grown on MGC, the crystal type is the same. Therefore, the Al ₂ O ₃ single crystal having a small difference in lattice constant is more stable, so that it grows preferentially over the Y ₃ Al ₅ O ₁₂ single crystal. Therefore, when MOCVD is performed, the pressure at the time of crystal growth and the V / III ratio are lowered to increase the surface migration, and the blue light emitting layer is grown mainly on the Al ₂ O ₃ single crystal. Can be laterally grown to obtain a flat blue light emitting layer.

Further, prior to epitaxial growth of a blue light-emitting layer may be performed a step of 5μm etching the Y ₃ Al ₅ O ₁₂ single crystal phase at the MGC wafer phosphoric acid based etchant. Thereby, the blue light emitting layer is laterally grown from the Al ₂ O ₃ single crystal phase, and a flat blue light emitting layer having a mirror surface can be obtained.

  Therefore, according to the present embodiment, a white light emitting element can be manufactured by the same process as that for manufacturing a normal blue light emitting element by epitaxially growing a blue light emitting layer directly on an MGC wafer.

According to the present embodiment, the blue light emitting layer is laterally grown from the Al ₂ O ₃ single crystal phase by etching the Y ₃ Al ₅ O ₁₂ single crystal phase of the MGC wafer before forming the blue light emitting layer. Therefore, a flat blue light emitting layer having a mirror surface can be obtained.

In the embodiment of the present invention, MGC is produced by a unidirectional solidification method. According solidification direction can be controlled crystal orientation Al ₂ O ₃ single crystal phase and Y ₃ Al ₅ O ₁₂ single crystal phase. Crystal orientation along the solidification direction Al ₂ O ₃ single crystal phase _{<1120>, Y 3 Al 5} O 12 single crystal phase <110>, or, Al ₂ O ₃ single crystal phase <0110>, Y ₃ The Al ₅ O ₁₂ single crystal phase is <110>. In addition, the Al ₂ O ₃ single crystal phase has a <0001> crystal orientation and the Y ₃ Al ₅ O ₁₂ single crystal phase has a <112> crystal orientation perpendicular to these directions.

[Third Embodiment]
In the third embodiment, a light-emitting device in which a light-emitting element in which a light-emitting layer is formed on an MGC is mounted on a package will be described. FIGS. 6A and 6B are cross-sectional views illustrating a part of a cross section of a light emitting device in which a light emitting element having a light emitting layer formed on MGC is mounted. The light emitting device shown in FIG. 6A has a concave portion for arranging the light emitting element, and the light emitting element is arranged on the die attach material 9 placed on the bottom surface of the concave portion with the light emitting layer 3 facing upward to emit light. An electrode provided on the layer 3 and a lead frame (not shown) are connected by a wire 8 and the light emitting element is sealed with a transparent resin 7 having a refractive index of 1.4 to 1.8. By sealing the light emitting element with the transparent resin 7, the blue light emitted from the light emitting layer 3 above the light emitting element and the yellow light emitted through the MGC 2 below the light emitting element are sufficiently mixed in the transparent resin 7. It is emitted as white light.

  The light-emitting device shown in FIG. 6B has a recess for arranging the light-emitting element, and the light-emitting element is flip-chip mounted on the gold bump 10 provided on the bottom surface of the recess with the light-emitting layer 3 facing down. is there. Thereby, the light radiated | emitted from the light emitting layer 3 passes MGC2, and white light is radiate | emitted from upper direction. The light-emitting device shown in FIG. 6 has a uniform color temperature orientation characteristic of about 6500 K, as compared with the case where an electrode is provided on the upper surface as shown in FIG. Further, by sealing the light emitting element with the transparent resin 7, more uniform white light that is sufficiently mixed in color can be obtained. In any of the embodiments, the light emitting element may be sealed with glass instead of the transparent resin 7.

  Therefore, according to the present embodiment, the light emitting element in which the light emitting layer 3 is formed on the MGC 2 is arranged on the bottom surface of the concave portion provided in the upper part of the light emitting device, and the concave portion is sealed with the transparent resin 7, thereby The blue light emitted from the light emitting layer 3 and the yellow light emitted through the MGC 2 below the light emitting element are sufficiently mixed in the transparent resin 7, so that more uniform white light can be obtained.

  According to the present embodiment, the light-emitting element in which the light-emitting layer 3 is formed on the MGC 2 is flip-chip mounted on the bottom surface of the recess provided in the upper portion of the light-emitting device with the light-emitting layer 3 facing down. The emitted light passes through the MGC 2, and blue light and yellow light are mixed in the MGC 2 to obtain white light from the upper direction. Moreover, since the color is sufficiently mixed in the transparent resin 7 by sealing the recesses with the transparent resin 7, more uniform white light can be obtained.

It is sectional drawing which shows the structure of the light emitting element in 1st Embodiment. It is a perspective view which shows the structure of MGC used for the light emitting element of FIG. It is sectional drawing which shows the mode of the growth of the light emitting layer in case the average period distance of MGC is large. The Y ₃ Al ₅ O ₁₂ single crystal phase MGC is a sectional view showing a state in which etching. It is sectional drawing which shows a mode that the light emitting layer was formed on MGC of FIG. It is sectional drawing which shows the structure of the light-emitting device which mounted the light emitting element in 1st Embodiment, (a) was mounted with the light emitting layer up, (b) was flip-chip mounted with the light emitting layer down. Show the state. It is sectional drawing which shows the structure of the conventional white light emitting diode. It is a schematic diagram which shows a mode that the emitted light of the conventional blue light emitting diode is converted into white using MGC as a light conversion element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light emitting element 2 ... MGC
21 ... Y ₃ Al ₅ O ₁₂ single crystal phase 22 ... Al ₂ O ₃ single crystal phase 3 ... luminescent layer 4 ... average period length 5 ... GaN crystal layer 7 ... transparent resin 8 ... wire 9 ... die attach material 10 ... gold bumps 71 ... Light-emitting element 72 ... Resin 73 ... Resin mold 80 ... MGC
81 ... Y ₃ Al ₅ O ₁₂ single crystal phase 82 ... Al ₂ O ₃ single crystal phase 83 ... blue light-emitting diode 84 ... blue light 85 ... yellow light 86 ... white light

Claims (14)

One or more kinds of single metal oxide single crystals and one or more kinds of composite metal oxide single crystals are formed in a continuous and sterically entangled manner and emit light to at least one of the metal oxides. A ceramic composite in which the body is doped;
A light emitting layer formed on the ceramic composite;
A light-emitting element including: The single metal oxide is Al ₂ O _3, the light emitting device of claim 1, wherein the composite metal oxide is Y ₃ Al ₅ O _12. The single crystal of Al ₂ O ₃ is aligned in the <1-100> direction, and the crystal plane of Al ₂ O _{3 on} the surface of the ceramic composite forming the light emitting layer is {0001}. The light emitting element as described in. The light emitting device according to claim 1, wherein the light emitting layer is a GaN-based light emitting layer, and the light emitter is Ce ³⁺ .   5. The light-emitting element according to claim 1, wherein an average distance at which the single crystal of the metal oxide appears periodically is 1 to 200 μm.   The light emitting element according to any one of claims 1 to 5, wherein the surface on which the light emitting layer of the ceramic composite is formed has one or more types of the metal oxide formed in a convex shape. The light emitting device according to claim 6, wherein the metal oxide formed in the convex shape is Al ₂ O ₃ .   The light emitting device according to claim 6 or 7, wherein the height of the convex shape is higher than 1 µm and within 10 µm. One or more kinds of single metal oxides and one or more kinds of complex metal oxides are continuously and sterically entangled with each other, and at least one kind of each metal oxide is doped with a light emitter. Epitaxially growing a light emitting layer on a wafer cut from the ceramic composite;
Cutting out a light emitting element from the wafer on which the light emitting layer is formed;
A method for manufacturing a light-emitting element, comprising: Further comprising the step of forming one or more types of the metal oxide into a convex shape by etching one surface of a wafer cut from the ceramic composite,
The method of manufacturing a light emitting element according to claim 9, wherein the step of growing the light emitting layer includes growing the light emitting layer on a surface on which the convex shape is formed.   A light-emitting device, wherein the light-emitting element according to claim 1 is sealed with a transparent resin or glass.   9. A light-emitting device, wherein the light-emitting element according to claim 1 is flip-chip mounted with the light-emitting layer facing downward.   The light emitting device according to claim 12, wherein the light emitting element is sealed with a transparent resin or glass. The light emitting device according to claim 11 or 13, wherein the transparent resin and the glass have a refractive index of 1.4 to 1.8.

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