Fluorescent device and fluorescence-emitting lighting device

Abstract

Fluorescent device (10, 20], comprising: a phosphor layer (1) a reflective film (2) provided on the phosphor layer (1); a distortion suppression layer (3) provided on the reflective film (2); and a support body (4) bonded to the distortion suppression layer (3) by direct bonding, wherein an excitation light (A) incident on the phosphor layer (1) is converted into a fluorescence (B), wherein the fluorescence (B) and the excitation light (A) are reflected by the reflective film (2) and emitted by the phosphor layer (1), wherein the reflective film (2) comprises a ferroelectric multilayer film (2), and wherein a coefficient of thermal expansion of a material of the distortion suppression layer (3) is greater than a coefficient of thermal expansion which is the largest among the coefficients of thermal expansion of materials forming the ferroelectric multilayer film (2).

Description

TECHNICAL AREA

[0001] The present invention relates to a phosphor device and a fluorescence-emitting lighting device. TECHNICAL BACKGROUND

[0002] Recently, an intensive study was conducted on headlights for a vehicle using a laser light source, one of which is a white light source consisting of a combination of a blue or ultraviolet laser and a phosphor. The luminance of the excitation light can be increased by condensing the laser light, and furthermore, the luminous intensity of the excitation light can also be increased by condensing multiple laser beams to achieve overlap with the phosphor. This allows for a simultaneous increase in luminous flux and brightness without altering the light-emitting area. Therefore, a white light source combining semiconductor lasers and a phosphor is an attractive light source to replace LEDs.For example, fluorescent glass for vehicle headlights is proposed to be “Lumiphous™” fluorescent glass from Nippon Electric Glass and monocrystalline YAG phosphors from the National Institute for Materials Science, Tamura Corporation and Koha Co. Ltd.

[0003] According to patent document 1, the use of monocrystalline YAG ensures that the conversion efficiency is not impaired even at higher temperatures, thus exhibiting high-efficiency phosphor properties and enabling applications with high power requirements. By inputting blue light at 450 nm as excitation light, this material can emit yellow light as its complementary color, resulting in white light. Therefore, the development of applications for projectors or spotlights was investigated.

[0004] The monocrystalline phosphor Ce:YAG was developed as a phosphor for lighting, in which Ce is doped in yttrium aluminum garnet (Y3Al5O). 12 :YAG). In the prior art, Ce-YAG phosphors were produced by synthesis through sintering or dispersion in a glass. With increasing power density of the excitation light, heat dissipation becomes more difficult, reducing efficiency, which is problematic.

[0005] Monocrystalline YAG doped with Ce has the property that the conversion efficiency is not affected despite heat generation in the crystal. It is therefore expected to be used as a light source for spotlights, projectors, or similar applications.

[0006] According to patent documents 2, 3, and 4, a lighting device with a phosphor reflector is disclosed. According to the device, a metal film is formed on the surface of a phosphor layer on the side opposite the incident surface onto which excitation light is incident, and the metal film is bonded to a heat-distributing body (support body). The material of the phosphor layer is specified as a glass material with phosphor dispersed therein, polycrystalline phosphor, or monocrystalline phosphor.

[0007] Patent document 5 discloses a lighting device with a reflective phosphor device. According to this system, a ferroelectric multilayer film is formed on a surface of the phosphor layer on the opposite side of an incident surface onto which excitation light strikes, and the ferroelectric multilayer film and heat-distributing bodies (support bodies) are bonded together. The ferroelectric multilayer film transmits the excitation light and reflects the fluorescence emitted by the phosphor layer. The ferroelectric multilayer film is formed by alternating lamination of layers with a low refractive index and layers with a high refractive index. Patent document 7 describes a radiation image conversion plate, a scintillator plate, and a radiation image sensor. Furthermore, patent document 8 discloses a fluorescent-emitting light source unit.Patent document 9 relates to a binder-free storage phosphor screen. Furthermore, patent document 10 describes a wavelength conversion element and a light-emitting device using the wavelength conversion element. QUOTE LIST PATENT DOCUMENT Patent document 1: JP 5 620 562 B1 Patent document 2: JP 5 530 165 B2 Patent document 3: JP 2012 - 129 135 A Patent document 4: JP 2013 - 120 713 A Patent document 5 WO 2015 / 045 976 A1 Patent document 6 WO 2016 / 167 071 A1 Patent document 7: US 2008 / 0 308 736 A1 Patent document 8: US 2016 / 0 040 857 A1 Patent document 9: US 2004 / 0 051 438 A1 Patent document 10: JP 2016 - 66 764 A BRIEF SUMMARY OF THE INVENTION

[0008] Furthermore, the applicant proposed a waveguide type of the phosphor device with a phosphor single crystal (patent document 6). However, the light propagating in an optical waveguide must be converted into fluorescence.

[0009] Based on the teachings of patent documents 3 to 5, the inventors attempted to form a reflective film on a phosphor layer and to bond the reflective film to a separate support body by direct bonding. However, uniform bonding across the entire bonding interface between the reflective film and support body could not be achieved, and bubbles could form. Since excitation light is irradiated onto the phosphor layer after the reflective film and support body have been bonded together, the intensity of the fluorescence emitted by the phosphor device can be affected. Because the in-plane deviation was observed in the phosphor layer during this phenomenon, it has been demonstrated that the color deviation occurs in the emitted fluorescence.

[0010] One object of the present invention is to provide, in a phosphor device comprising a phosphor layer made of a phosphor glass or phosphor single crystal, a reflective film on the phosphor layer and a support body, in order to improve the bonding state of the reflective film and the support body and to improve the intensity of the fluorescence emitted by the phosphor device.

[0011] The present invention provides a fluorescent device comprising: a phosphor layer; a reflective film provided on the phosphor layer; a distortion suppression layer provided on the reflective film; and a support body bonded to the distortion suppression layer by direct bonding, wherein excitation light incident on the phosphor layer is converted into fluorescence, wherein the fluorescence and the excitation light are reflected by the reflective film and emitted by the phosphor layer, wherein the reflective film comprises a ferroelectric multilayer film, and where a coefficient of thermal expansion of a material of the distortion suppression layer is greater than a coefficient of thermal expansion that is the largest among the coefficients of thermal expansion of materials forming the ferroelectric multilayer film.

[0012] The inventors investigated the cause of blistering on the bonding surface of the support body and the reduction in the intensity of the fluorescence reflected by the device when the reflective film is formed on the phosphor layer and bonded directly to the separate support body. The inventors then discovered the following.

[0013] Since the reflective layer is a ferroelectric multilayer film, the ferroelectric film forms only on a primary surface of the phosphor layer. Because the temperature is elevated during film formation, deformation occurs due to the difference in the coefficients of thermal expansion between the phosphor layer and the ferroelectric multilayer film when the temperature returns to ambient after film formation. Consequently, if the phosphor layer and support are bonded by direct bonding, the direct bond with the support cannot be uniformly applied across the entire surface due to this deformation. Bubbles can form in areas where the bond is not established. Furthermore, it has been observed that the conversion efficiency is reduced by the influence of residual stresses in the phosphor layer, thereby lowering the fluorescence intensity.

[0014] Similarly, if the reflective film consists of a metal film, the metal film forms only on the primary surface of the phosphor layer. Since the temperature is elevated during film formation, deformation occurs due to the difference in the coefficients of thermal expansion between the phosphor layer and the metal film when the temperature returns to ambient after film formation. However, the direction of this deformation is opposite to that observed during the formation of the ferroelectric multilayer film. Therefore, if the phosphor layer and support are bonded by direct bonding, this deformation prevents a uniform bond across the entire surface. Bubbles can form in areas where the bond is not established.Furthermore, it is noted that the conversion efficiency is worsened by the effect of residual stresses in the phosphor layer, thereby reducing the intensity of the fluorescence.

[0015] The inventors then attempted to form a reflective film on the phosphor layer and a distortion-suppressing layer on the reflective film, so that the deformation of the phosphor layer is reduced and the phosphor layer is bonded to the support body by direct bonding. This is found to suppress bubble formation at the bonding interface with the support body, prevent the deterioration of conversion efficiency due to stress, and improve the intensity of the fluorescence reflected by the device. The present invention has thus been implemented. BRIEF DESCRIPTION OF THE DRAWINGS Fig.Figure 1 is a diagram schematically representing a fluorescent device 10 according to an embodiment of the present invention. Fig. Figure 2 is a diagram schematically illustrating a fluorescent device 9, which does not represent an embodiment of the present invention. Fig. Figure 3(a) shows the state in which a ferroelectric multilayer film 2A is formed on a phosphor layer 1A, Fig. 3(b) shows the state after cooling of the phosphor layer of Fig. 3(a) and Fig. Figure 3(c) shows the state in which a phosphor layer 1B is bonded to a support body 4 with a provided ferroelectric multilayer film 2B. Fig. 4(a) shows the state in which a metal film 5A is formed on a phosphor layer 1A, Fig. 5(b) shows the state after the phosphor layer has cooled. Fig. 4(a) and Fig.Figure 4(c) shows the state in which a phosphor layer 1C with a metal film 5B formed on it is bonded to the support body 4. Fig. Figure 5(a) shows the state in which a ferroelectric multilayer film 2A is formed on the phosphor layer 1A, Fig. 5(b) shows the state after the phosphor layer has cooled. Fig. 5(a), Fig. Figure 5(c) shows the condition in which a distortion suppression layer 3 is provided on the ferroelectric multilayer film 2, and Fig. Figure 5(d) shows the state in which a distortion suppression layer 4 is bonded to the support body 1 by direct bonding. Fig. Figure 6(a) shows the state in which a metal film 5A is formed on the phosphor layer 1A, Fig. 6(b) shows the state after the phosphor layer has cooled. Fig. 6(a), Fig. Figure 6(c) shows the condition in which the distortion suppression layer 3 is provided on the metal film 5, and Fig. Figure 6(d) shows the state in which the distortion suppression layer 4 is bonded to the support body 1 by direct bonding. Fig. Figure 7 is a diagram that schematically represents a device 20 according to yet another embodiment of the present invention, in which a partial transmission film 15 is provided on the phosphor layer 1. EXECUTIONAL FORMS FOR IMPLEMENTING THE INVENTION

[0016] Fig. Figure 1 is a diagram schematically representing a fluorescent device 10 according to an embodiment of the present invention.

[0017] In the phosphor device 10, a ferroelectric multilayer film 2 is provided on a main surface 1b of a phosphor layer 1, and a distortion suppression layer 3 is provided on a main surface 2b of the ferroelectric multilayer film 2. A main surface 3b of the distortion suppression layer 3 is bonded to a main surface 4a of a support body 4 by direct bonding. 4b represents a bottom surface of the support body 4. Furthermore, 2a represents a main surface of the ferroelectric multilayer film 2, and 3a represents a main surface of the distortion suppression layer 3.

[0018] When an excitation light A is incident on the main surface 1a of the phosphor layer 1, part of the excitation light is converted into fluorescence light, which passes through the main surface 2a onto the ferroelectric multilayer film 2. The remaining excitation light and the fluorescence are reflected into the ferroelectric multilayer film 2, pass through the phosphor layer 1 again, as indicated by arrow B, and are emitted from the main surface 1a.

[0019] Fig. Figure 2 is a diagram schematically illustrating a fluorescent device 9, which does not represent an embodiment of the present invention.

[0020] In the phosphor device 9, a metal film 5 is provided on a main surface 1b of a phosphor layer 1, and a distortion suppression layer 3 is provided on a main surface 5b of the metal film 5. The main surface 3b of the distortion suppression layer 3 is bonded to a main surface 4a of a support body 4 by direct bonding. 4b represents a bottom surface of the support body 4. 5a represents the main surface of the metal film 5, and 3a represents the main surface of the distortion suppression layer 3.

[0021] When an excitation light A strikes the main surface 1a of the phosphor layer 1, part of the excitation light A is converted into fluorescence. The excitation light and fluorescence are reflected from the main surface 5a of the metal film 5, pass through the phosphor layer 1 again as shown by arrow B, and are emitted from the main surface 1a.

[0022] The effect of the present invention is described in more detail below.

[0023] The inventors attempted to form a ferroelectric multilayer film 2A on a phosphor layer 1A and to bond the ferroelectric multilayer film 2A to a separate support body 4 by direct bonding, as for example in Fig. Figure 3 illustrates this. The inventors then investigated the cause of the bubbles being generated on the bonding surface 4a of the support body 4 and the reduction in the intensity of the fluorescence reflected by the device. The following results are thus obtained.

[0024] In the event that the reflective film is the ferroelectric multilayer film 2A, the ferroelectric multilayer film 2A is formed only on the first main surface 1b of the phosphor layer 1. Even if the laminate is heated during the film formation step (at high temperature), as in Fig.3(a) shown, it is due to the difference in the coefficients of thermal expansion of the phosphor layer 1B and the ferroelectric multilayer film 2B after cooling, as shown in Fig. 3(b) shows a deformation. Since the coefficient of thermal expansion of the phosphor layer is higher than that of the ferroelectric multilayer film, the degree of shrinkage of the phosphor layer 1B is typically greater than that of the ferroelectric multilayer film 2B during the cooling process. This causes the device to warp so that the ferroelectric multilayer film 2B protrudes.

[0025] This can, as in Fig.Figure 3(c) shows that if the phosphor layer 1B and the bonding surface 4a of the support body 4 are bonded by direct bonding, distortion can make it difficult to perform direct bonding over the entire surface of the support body. This can lead to bubbles forming on the bonding surface of the support body. If the direct bonding is completed, the conversion efficiency is found to be degraded, and the intensity of the fluorescence is reduced by the effect of residual stresses in the phosphor layer 4. It is generally known that trapping by lattice defects reduces the conversion efficiency. Recently, it has been shown that when milling the YAG single crystal, defect values ​​can be introduced on the particle surfaces during processing, thereby reducing the conversion efficiency.It is therefore assumed that, since the residual stresses are generated in the phosphor layer, microcracks can be caused by the residual stresses, thereby reducing the conversion efficiency.

[0026] Furthermore, if the reflective film is the metal film, the metal film 5A is formed only on the first main surface 1b of the phosphor layer 1A, as shown in Fig. 4(a) is shown. Even if the laminate is exposed during the film formation step (at high temperature), as in Fig. As shown in 4(a), if the surface is flat, deformation occurs due to the difference in the coefficients of thermal expansion of the phosphor layer 1C and the metal film 5B after cooling, as shown in Fig.Figure 4(b) illustrates this. Since the coefficient of thermal expansion of the phosphor layer is lower than that of the metal film, the degree of shrinkage of the phosphor layer 1C is typically less than that of the metal film 5B during the cooling step. This causes the device to warp, resulting in a depression in the surface of the metal film 5B.

[0027] This can, as in Fig. Figure 4(c) shows that if the phosphor layer 1C and the bonding surface 4a of the support body 4 are bonded by direct bonding, it may be difficult to complete the direct bond uniformly over the entire surface of the support body due to deformation. This can lead to the formation of bubbles on the bonding surface of the support body. If the direct bonding is completed, the conversion efficiency is reduced and the intensity of the fluorescence is decreased due to the effect of residual stresses in the phosphor layer 4.

[0028] The inventors then attempted to form the reflective film on the phosphor layer and the distortion-suppressing layer on the reflective foil in such a way as to reduce the deformation of the phosphor layer and to bond the phosphor layer to the support body through direct bonding. The results showed that the bond to the bonding surface of the support body is formed uniformly, bubble formation is suppressed, the deterioration of the stress-induced conversion efficiency is prevented, and the intensity of the fluorescence reflected by the device is improved.

[0029] That is, in the case that the reflective film is the ferroelectric multilayer film, as described above, the deformation after the cooling step occurred due to the difference in the coefficients of thermal expansion between phosphor layer 1B and ferroelectric multilayer film 2B, as shown in Fig. 5(b) is shown. Since the distortion suppression layer 3 is formed on the main surface 2b of the ferroelectric multilayer film 2B, the distortion of the ferroelectric multilayer film 2 and the phosphor layer 1 is then prevented according to the present invention as shown in Fig. 5(c) is shown to be suppressed in such a way that the flatness of the main surface 3b of the warp suppression layer 3 is improved. Since in this state the warp suppression layer 3 is bonded by direct bonding, as in Fig. As shown in Figure 5(d), with the support body 4 bonded, it turns out that the bubbles on the bonding surface of the support body can be suppressed and the intensity of the fluorescence reflected by the device is improved as described above.

[0030] If the reflective film is the metal film, as described above, deformation due to the difference in the coefficients of thermal expansion between phosphor layer 1C and metal film 5B continued to occur after the cooling step, as shown in Fig. 6(b) is shown. Since the distortion suppression layer 3 is formed on the main surface 5b of the metal film 5B, the deformation of the metal film 5 and the phosphor layer 1 is then as shown in Fig. 5(c) is shown to be suppressed in such a way that the flatness of the main surface 3b of the warp suppression layer 3 is improved. Since in this state the warp suppression layer 3 is bonded to the support body 4 by direct bonding, as in Fig. As shown in Figure 5(d), it turns out that the bubbles on the bonding surface of the support body can be suppressed and the intensity of the fluorescence reflected by the device is improved.

[0031] Depending on the preferred embodiment, a partial transmission film is provided which transmits part of the excitation light to the phosphor layer on the opposite side of the reflective film. By providing the transmission film, the excitation light is thus introduced into the phosphor layer after passing through the partial transmission film.

[0032] That means according to the in Fig.In the device 20 shown in Figure 7, the ferroelectric multilayer film 2 (or metal film 5) is provided on the main surface 1b of the phosphor layer 1, and the distortion suppression layer 3 is provided on the main surface 2b (5b) of the ferroelectric multilayer film 2 (metal film 5). A partial transmission film 15 is provided on the main surface 1a of the phosphor layer 1 on the side opposite the ferroelectric multilayer film 2. The main surface 3b of the distortion suppression layer 3 is bonded to the main surface 4a of the support body 4 by direct bonding.

[0033] The excitation light A is incident on the main surface 15a of the partial transmission film 15. Part of the excitation light is reflected by the partial transmission film, and the remaining part of the light is incident on the main surface 1a of the phosphor layer 1. The excitation light A incident on the phosphor layer 1 is reflected by the ferroelectric multilayer film 2 (metal film 5) as shown by arrow C and then by the main surface 15b of the partial transmission film 15 as shown by arrow D. The excitation light A propagates within the phosphor layer 1 and is gradually converted into fluorescence as it is repeatedly subjected to multiple reflections as shown by arrows C and D. The remaining excitation light and fluorescence light pass through the phosphor layer 1 again as shown by arrow B. The light emitted from the main surface 1a of the phosphor layer is transmitted through the partial transmission film 15 and is emitted to the outside of the device as shown by arrow B.

[0034] A partial transmission film is a film through which a portion of the excitation light is transmitted, while the remaining portion is reflected. Multiple reflections occur between the incident surface of the excitation light and the opposite surface of the phosphor layer. This allows for a uniform luminance distribution of the fluorescence, even with a planar conversion efficiency, thanks to the uniformity of the phosphor layer. As a result, white light without color dispersion can be achieved for illumination purposes.

[0035] Furthermore, the reflective film can be applied to the first main surface and the partial transmission film to the second main surface of the phosphor layer, thus partially offsetting both stresses and reducing the deformation of the phosphor layer. The distortion suppression layer is further shaped to achieve a uniform direct bonding interface.

[0036] The embodiments of the present invention are described in detail below.

[0037] Although the phosphor forming the phosphor layer is not limited as long as it can convert the excitation light into fluorescence, the phosphor can be a phosphor glass, a phosphor single crystal, or a phosphor polycrystal.

[0038] Fluorescent glass is produced by diffusion of rare earth metals in a base glass.

[0039] The glass used as a base can be an oxide glass containing silicon dioxide, boron oxide, calcium oxide, lanthanum oxide, barium oxide, zinc oxide, phosphorus oxide, aluminum fluoride, magnesium fluoride, calcium fluoride, strontium fluoride or barium chloride.

[0040] Although the rare earth metals diffused in the fluorescent glass are preferably Tb, Eu, Ce and Nd, the rare earth metal ions can be La, Pr, Sc, Sm, Er, Tm, Dy, Gd or Lu.

[0041] Y3Al5O is a single phosphor crystal. 12 , Ba5Si 11 Al7N 25 , and Tb3Al5O 12 preferred. A portion of the Y (yttrium) sites of Y3Al5O 12 can be replaced by Lu. Furthermore, a dopant doped in the phosphor single crystal can preferably be a rare earth ion and preferably Tb, Eu, Ce or Nd, although the dopant contains La, Pr, Sc, Sm, Er, Tm, Dy, Gd or Lu.

[0042] The following polycrystalline phosphors are listed: TAG (terbium aluminum garnet), Sialon, BOS (barium orthosilicate), and YAG (yttrium aluminum garnet). Some of the Y (yttrium) ions in YAG can be replaced by Lu.

[0043] A dopant doped into the polycrystalline phosphor may preferably be a rare earth ion and preferably be Tb, Eu, Ce or Nd, although the dopant may include La, Pr, Sc, Sm, Er, Tm, Dy, Gd or Lu.

[0044] The thickness of the phosphor layer can preferably be 30 µm or greater, and more preferably 50 µm or greater, to convert the excitation light into fluorescence with a sufficiently high efficiency. Furthermore, if the phosphor layer is too thick, the excitation light or fluorescence is scattered or emitted at the substrate's side surface, leading to attenuation. Therefore, the thickness of the phosphor layer can preferably be 300 µm or less, and more preferably 250 µm or less.

[0045] The thickness of the phosphor layer represents a dimension of the phosphor layer in a direction perpendicular to the bonding surface of the support body.

[0046] The reflective film on the phosphor layer is not particularly limited as long as it can reflect fluorescence through the phosphor layer. It is not necessary for the reflective film to reflect the excitation light by total internal reflection, and the reflective film can transmit some of the excitation light.

[0047] According to the present invention, the reflective film is a ferroelectric multilayer film.

[0048] Since the reflective film is a ferroelectric multilayer film, it is possible to avoid absorption and reflect 100 percent of the incident light in order to obtain the reflected light without loss.

[0049] The reflectivity of the excitation light by the reflective film is 90 percent or more, and preferably 95 percent or more. The excitation light can be subjected to total internal reflection.

[0050] The ferroelectric multilayer film is formed by alternating lamination of a low-refractive-index material and a high-refractive-index material. The high-refractive-index material includes TiO₂, Ta₂O₃, ZnO, Si₃N₄, and Nb₂O₅. The low-refractive-index material includes SiO₂, MgF₂, and CaF₂.

[0051] The number of layers and the total thickness of the ferroelectric multilayer film are selected according to the wavelength of the fluorescence to be reflected.

[0052] Not belonging to the present invention, the reflective film is a metal film. The material of the metal film can preferably be as follows. (i) A single-layer film made of Al, Ag, Au, etc. (ii) A multi-layered film made of Al, Ag, Au, etc.

[0053] To ensure adhesion of the reflective film and phosphor substrate, to prevent separation and to prevent ion migration, a buffer layer of Cr, Ni, Ti, Pt or the like can be provided between the metal film and the phosphor layer.

[0054] Although the thickness of the metal film is not particularly limited as long as it can reflect the fluorescence, the thickness of the metal film can preferably be 0.05µm or greater and preferably 0.1µm or greater.

[0055] The process for producing the ferroelectric multilayer film, the metal film, and the distortion suppression layer is not particularly limited and includes the vapor deposition process, the sputtering process, and the CVD process. In the case of vapor deposition, ion aids can be added to promote film formation.

[0056] The material of the support body can preferably be a material with high thermal conductivity, allowing for easy achievement of a high surface flatness. In this regard, the material of the support body can preferably be aluminum oxide, aluminum nitride, silicon carbide, silicon, or sapphire.

[0057] A partial transmission film is a film that reflects part of the excitation light and transmits the remainder. In particular, the reflectance of the partial transmission film with respect to the excitation light can preferably be 9 percent or higher, and more preferably 50 percent or higher.

[0058] The material of the partial transmission film comprises the metal film or ferroelectric multilayer film for the reflective film as described above. Furthermore, for the transmission of a portion of the excitation light, the thickness of the metal film can preferably be smaller, and particularly preferably 0.1 µm or less. Additionally, the number of layers of the ferroelectric multilayer film can preferably be smaller, and particularly preferably 10 or less.

[0059] According to a preferred embodiment, the coefficient of thermal expansion of the support material can preferably be between 50 and 150 to suppress the reduction in conversion efficiency due to deformation after bonding with the phosphor, provided that 100 is assigned to the coefficient of thermal expansion of the phosphor layer material. From this perspective, the support material can preferably be aluminum oxide, aluminum nitride, or sapphire.

[0060] With regard to heat dissipation, the thickness of the support body can preferably be 200 µm or greater. Furthermore, with regard to reducing the size of the device, the thickness of the support body can preferably be 1000 µm or less.

[0061] The material for the distortion suppression layer provided on the reflective film is selected to suppress deformation after the reflective film has been formed on the phosphor layer.

[0062] According to the present invention, the reflective film is the ferroelectric multilayer film and the coefficient of thermal expansion of the material of the distortion suppression layer is greater than the coefficient of thermal expansion of the material whose coefficient of thermal expansion is greatest among the materials forming the ferroelectric multilayer film.

[0063] In this case, the coefficient of thermal expansion of the distortion suppression layer can preferably be 150 to 600 and more preferably 250 to 500, provided that 100 is assigned to the coefficient of thermal expansion of the material with the maximum coefficient of thermal expansion among the materials forming the ferroelectric multilayer film.

[0064] Not belonging to the present invention, the reflective film is a metal film and the coefficient of thermal expansion of the distortion suppression layer is smaller than that of the material forming the metal film.

[0065] In this case, provided that 100 is assigned to the coefficient of thermal expansion of the material of the metal film, the coefficient of thermal expansion of the material of the distortion suppression layer can preferably be 25 to 70 and more preferably 30 to 50.

[0066] The coefficient of thermal expansion mentioned in the description is defined as a linear coefficient of thermal expansion in the direction of the plane of the substrate surface at 25°C.

[0067] Furthermore, the coefficient of thermal expansion of the distortion suppression layer can be kept smaller than the coefficient of thermal expansion of the phosphor layer, so that the effect of suppressing deformation can be made even more pronounced.

[0068] Furthermore, according to a preferred embodiment, the coefficient of thermal expansion of the distortion suppression layer is between the coefficient of thermal expansion of the phosphor layer and the coefficient of thermal expansion of the reflective film.

[0069] Furthermore, according to a preferred embodiment, the coefficient of thermal expansion of the distortion suppression layer is 50 to 150, provided that 100 is assigned to the coefficient of thermal expansion of the phosphor layer material. This makes it possible to easily suppress distortion of the phosphor layer. Provided that 100 is assigned to the coefficient of thermal expansion of the phosphor layer material, the coefficient of thermal expansion of the distortion suppression layer can preferably be 75 to 125.

[0070] The coefficients of thermal expansion of the preferred materials are shown below. Table 1 material coefficient of thermal expansion ×10 -6 / K Fluorescent layer YAG 8 Reflective film (metal) Al 23,2 AG 19,0 Au 14,2 Reflective film (ferroelectric multilayer film) TiO2 2,1 SiO2 0,7 Warpage suppression layer Al2O3 7,2 SiC 4,4 Zr2O 10,5 AIN 4,6 Note 7,0 Ta 6,3 Mon 5,3 W 4,5

[0071] According to the present invention, the support body is bonded to the distortion suppression layer by direct bonding.

[0072] Although direct bonding is generally divided into metal / covalent bonding and diffusion bonding, this article focuses on metal / covalent bonding, in which a surface activation treatment is performed under high vacuum. Furthermore, according to the present invention, surface activation bonding is preferred with regard to preventing contamination of the bonding interface by atoms other than those forming the laminated layer and a support structure.

[0073] Surface activation bonding is described below. Argon ions are irradiated onto a substrate with high flatness to remove impurity atoms from the surface, leaving dangling or free bonds. This results in a well-activated surface state, making it possible to bond to a workpiece at ambient temperature. Various types of materials can be bonded together in this way. Furthermore, an amorphous layer may remain along the bonding surface.

[0074] Furthermore, atomic diffusion bonding involves the formation of a metal film, such as titanium, on the support structure, followed by the bonding process. As a surface activation bonding method, it is possible to perform the bonding at a temperature low of ambient temperature, not exceeding 400°C. However, crystallized metal oxide remains, and an amorphous layer does not form. Therefore, thermal expansion at the bonding interface can lead to problematic thermal stress.

[0075] According to the present embodiment, the argon ion irradiation method is modified to prevent contamination of the interface of a vacuum chamber-forming metal material and to prevent contamination of the amorphous layer by atoms other than those forming the distortion suppression layer and the support body. This improves the stress relief effect.

[0076] Furthermore, the duration of the irradiation of the argon ions is controlled in such a way that it is possible to control the thickness of the amorphous layer.

[0077] A semiconductor laser made of a GaN material is preferable as a light source for exciting the phosphor and illuminating it. Alternatively, a light source such as a one-dimensional laser array can be implemented. This light source can be a superluminescent diode or a semiconductor optical amplifier (SOA). An LED can also be used, or excitation light from a light source can be directed onto the phosphor device via an optical fiber.

[0078] Although there are no particularly limited methods for generating white light from the semiconductor laser and the phosphor, the following methods are conceivable.

[0079] Method for generating a yellow fluorescent beam using a blue laser and phosphor, thereby producing white light.

[0080] Method for generating red and green fluorescent beams using a blue laser and phosphor, thereby producing white light.

[0081] Method for generating red, blue and green fluorescent beams from a blue laser or ultraviolet laser using phosphor, thereby producing white light.

[0082] Method for generating blue and yellow fluorescence beams from a blue laser or ultraviolet laser using phosphor, thereby producing white light.

[0083] Furthermore, the respective end faces of the light source element and the phosphor assembly can be cut at an angle to suppress reflection from the end face. Bonding between the phosphor assembly and the support body can be either adhesive bonding or direct bonding. The phosphor element can be formed on the support body using a film formation process such as sputtering or CVD. EXAMPLES

[0084] (Example 1: Case where the reflective film is a multi-layered film) A fluorescent device 10 was used according to Fig. 1 by procedure as in Fig. 5 shown manufactured.

[0085] In particular, a ferroelectric multilayer film 2B was formed on a phosphor layer 1A made of monocrystalline Ce-doped YAG (yttrium aluminum garnet) by an ion-assisted vapor deposition system. The ferroelectric multilayer film 2B consists of alternating low-refractive-index and high-refractive-index layers. The low-refractive-index layers are made of SiO₂, the high-refractive-index layers of TiO₂, and the total number of low- and high-refractive-index layers is 69. Furthermore, the total thickness of the low-refractive-index layers is 3.3 µm, the total thickness of the high-refractive-index layers is 1.8 µm, and the total thickness of the ferroelectric multilayer film is 5 µm.According to this ferroelectric multilayer film, in the case where the angle of incidence of the excitation light is 45°, the reflectance at a wavelength of 450nm was higher than 99.5 percent and the reflectance at a wavelength of 580nm was 98 percent.

[0086] In the above case, the coefficients of thermal expansion of SiO2 and TiO2, which form the ferroelectric multilayer film, are 0.7 × 10 -6 / K and 2.1×10 -6 / K, which is lower than the coefficient of thermal expansion of the monocrystalline YAG phosphor layer of 8×10 -6 / K is. Therefore, a compressive stress was applied to the phosphor layer after vapor deposition, so that the deformation greater than 100µm was generated in the phosphor device of φ 3 inch.

[0087] The distortion suppression layer 3, made of Al₂O₃, was then formed by sputtering. The coefficient of thermal expansion of Al₂O₃ is higher than that of TiO₂, whose coefficient of thermal expansion is higher in both types of the ferroelectric material forming the ferroelectric multilayer film. The coefficient of thermal expansion of Al₂O₃ was 7.2 × 10⁻⁶ -6 The coefficient of thermal conductivity (K) and the thickness were kept at 2 µm. As a result, the deformation of the phosphor layer was reduced to 10 µm or less.

[0088] The sapphire support structure and the distortion-suppressing layer on the phosphor layer were then bonded by direct bonding (surface activation process) at ambient temperature. Microscopic observation of the bonding interface revealed no bubbles at the direct bond interface. Subsequently, the bonded phosphor layer underwent optical polishing to a thickness of 100 µm. The thickness deviation of the phosphor layer was measured to be within ±0.25 µm.

[0089] Finally, the bonded body was cut to a size of 5×5 mm using a cube system to create the reflection pattern of the phosphor devices. A 30 mW blue semiconductor laser was projected onto the resulting phosphor device at a 45° angle to the phosphor. The internal quantum efficiency at this point was over 90 percent. Furthermore, no color deviations were observed. (Comparative example 1: Case where reflective film is ferroelectric multilayer film)

[0090] The fluorescent device was installed according to the instructions. Fig. 3 methods shown.

[0091] As in Example 1, the ferroelectric multilayer film 2B was formed on the phosphor layer of monocrystalline Ce-doped YAG (yttrium aluminum garnet) by an ion-assisted vapor deposition system. A compressive stress was then applied to the phosphor layer after vapor deposition, resulting in a deformation greater than 100 µm in the phosphor layer of φ 3 inches.

[0092] The sapphire support body 4 and the distortion suppression layer 2B were then bonded by direct bonding (surface activation process) at ambient temperature. Microscopic observation of the bonding interface revealed numerous bubbles at the bonding interface of the direct bond.

[0093] The bonded phosphor layer was then subjected to optical polishing with a thickness of 100 µm. The thickness deviation of the phosphor layer was measured at ±5 µm.

[0094] Finally, the bonded body was cut to a size of 5×5 mm using a cube system to create the reflection pattern of the phosphor devices. A 30 mW blue semiconductor laser was projected onto the resulting phosphor device at a 45° angle to the phosphor layer. The internal quantum efficiency at this point was over 80 percent. A deviation in color tones was still observed. (Example 2 as a reference example: case where the reflective film is a metallic film)

[0095] A fluorescent device 9 was shown in Fig. 2, by means of procedures as described in Fig. 6 shown manufactured.

[0096] In particular, a metal film (aluminum film) 5B was formed on a phosphor layer of monocrystalline Ce-doped YAG (yttrium aluminum garnet) by a sputtering system to a thickness of 2 µm. The aluminum film exhibits a reflectance of 91 percent at a wavelength of 450 nm and 91 percent at a wavelength of 580 nm. In the above case, the coefficients of thermal expansion of the monocrystalline YAG phosphor layer and the aluminum film were 8 × 10 -6 / K or 23.2×10 -6 / K. Therefore, a compressive stress was applied to the substrate device after sputtering, so that a deformation greater than 100µm was produced in the phosphor layer of φ 3 inch.

[0097] The distortion suppression layer 3, made of Al₂O₃, was then formed by sputtering. The coefficient of thermal expansion of Al₂O₃ is lower than that of the aluminum film. The coefficient of thermal expansion of Al₂O₃ was 7.2 × 10⁻⁶. -6The coefficient of thermal conductivity (K) and the thickness were kept at 2 µm. As a result, the deformation of the phosphor layer was reduced to 10 µm or less.

[0098] The sapphire support body 4 and the distortion suppression layer 3 were then bonded by direct bonding (surface activation process) at ambient temperature. Microscopic observation of the bonding interface revealed no bubbles at the direct bond interface. Subsequently, the bonded phosphor layer was optically polished to a thickness of 100 µm. The thickness deviation of the phosphor layer was measured to be within ±0.25 µm.

[0099] Finally, the bonded body was cut to a size of 5×5 mm using a dicing system to create the reflection pattern of the phosphor devices. A 30 mW blue semiconductor laser was projected onto the resulting phosphor device at a 45° angle to the phosphor layer. The internal quantum efficiency at this point was over 90 percent. Furthermore, no color deviations were observed. (Comparative example 2: Case where the reflective film is a metal film)

[0100] The fluorescent device was installed according to the specifications in Fig. 4 methods shown.

[0101] As in Example 2, the metal film on the phosphor layer of monocrystalline Ce-doped YAG (yttrium aluminum garnet) was formed by an ion-assisted vapor deposition system. A compressive stress was then applied to the phosphor layer after vapor deposition, resulting in a deformation greater than 100 µm in the phosphor substrate of φ 3 inches.

[0102] The sapphire body and the phosphor substrate were then bonded by direct bonding (surface activation process) at ambient temperature. Microscopic observation of the bonding interface revealed numerous bubbles at the interface of the direct bond. Subsequently, the bonded phosphor layer underwent optical polishing to a thickness of 100 µm. The thickness deviation of the phosphor layer was measured at ±5 µm.

[0103] Finally, the bonded body was cut to a size of 5×5 mm using a dicing system to create the reflection pattern of the phosphor devices. A 30 mW blue semiconductor laser was projected onto the resulting phosphor device at a 45° angle to the phosphor layer. The internal quantum efficiency at this point was over 80 percent. A deviation in color tones was still observed. (Example 3: Case where the reflective film is a ferroelectric multilayer film and a partial transmission film is present on the opposite side of the reflective film)

[0104] A fluorescent device 20 was shown in Fig. 7, produced by methods as in Example 1.

[0105] However, the thickness of the phosphor layer 1 was set to 50 µm and the thickness deviation of the phosphor layer 1 to ±0.25 nm. A partial transmission film 15 was formed on a polished main surface 1a of the phosphor layer. The partial transmission film was formed from a ferroelectric multilayer film. Specifically, the low-refractive-index layers were made of SiO₂, the high-refractive-index layers of TiO₂, and the total number of low- and high-refractive-index layers was 5. According to this ferroelectric multilayer film, the reflectance in a wavelength range of 430 nm to 470 nm was 20 percent or higher, and the reflectance was 40 percent when the wavelength was 450 nm.

[0106] Finally, the bonded body was cut to a size of 5×5 mm using a dicing system to create the reflection pattern required for the phosphor devices. A 30 mW blue semiconductor laser was projected onto the resulting phosphor device at a 45° angle to the phosphor layer. The internal quantum efficiency at this point was over 90 percent. Furthermore, no color deviations were observed.

Claims

[1] A phosphor device (10, 20) comprising: a phosphor layer (1]; a reflective film (2) provided on the phosphor layer (1); a distortion suppression layer (3) provided on the reflective film (2); and a support body (4) bonded to the warpage suppression layer (3) by direct bonding, wherein an excitation light (A) incident on the phosphor layer (1) is converted into a fluorescence (B), wherein the fluorescence (B) and the excitation light (A) are reflected by the reflective film (2) and emitted by the phosphor layer (1), wherein the reflective film (2] comprises a ferroelectric multilayer film (2], and wherein a thermal expansion coefficient of a material of the warpage suppression layer (3) is larger than a thermal expansion coefficient which is the largest among the thermal expansion coefficients of materials constituting the ferroelectric multilayer film (2). [2] Device (10, 20] according to claim 1, wherein the phosphor layer (1] comprises a phosphor glass or a phosphor single crystal. [3] The device (20) according to claim 1 or 2, further comprising a partial transmission film (15) which partially transmits the excitation light (A) and is provided on the phosphor layer (1) on a side opposite to the reflective film (2), wherein the excitation light (A) is incident on the phosphor layer (1) after the excitation light (A) has passed through the partial transmission film (15). [4] Device (10, 20] according to one of claims 1 to 3, wherein a ratio of thermal expansion coefficient of the warpage suppression layer (3] : thermal expansion coefficient of a material of the phosphor layer (1] is 50 to 150 :

100. [5] Device (10, 20] according to one of claims 1 to 4, wherein the ferroelectric multilayer film (2] comprises a low refractive index material and a high refractive index material, wherein the low refractive index material comprises SiO2, MgF2 or CaF2, and wherein the high refractive index material comprises TiO2, Ta2O5, Ta2O3, ZnO, Si3N4 or Nb2O5. [6] Device (10, 20] according to one of claims 1 to 5, wherein the distortion suppression layer (3] comprises Al2O3, SiC, Zr2O, AlN, Nb, Ta, Mo or W. [7] An illumination device comprising a light source that oscillates an excitation light (A) and a phosphor device (10, 20), wherein the phosphor device (10, 20) comprises the phosphor device (10, 20) according to any one of claims 1 to 6.

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