Dielectic film coating for ceramic full conversion tiles

Abstract

Wavelength converter including: a phosphor layer; and a filter layer where the filter layer is attached directly to the phosphor layer, wherein the wavelength converter has a total thickness between 20 µm and 80 µm, wherein the filter layer comprises at least two different metal oxides selected from the group consisting of SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3.

Description

SPECIALIZATION

[0001] The present invention relates to wavelength converters, light-emitting device arrangements and methods for manufacturing wavelength converters and light-emitting devices. BACKGROUND

[0002] Several embodiments of phosphor wavelength converters exist in the prior art. Often, ceramic phosphor materials are used to convert light of a specific wavelength into a specific additional wavelength. However, some of these ceramic phosphor materials exhibit scattering. Such ceramic phosphor materials are known, for example, from DE 10 2014 107 972 A1. US 2012 / 228 653 A1 and EP 1 958 269 A1 describe various methods for manufacturing phosphor wavelength converters.

[0003] In other designs, for example, amber-colored ceramics with the composition (Sr,Ba)2Si5N8:Eu are used for full-conversion LED applications, where the blue light from a blue LED chip is completely or almost completely absorbed by an amber-colored ceramic plate converter on the top of the LED chip and re-emitted as amber light at longer wavelengths. Full-conversion amber LEDs have a wide range of applications, such as turn signals and taillights in automobiles, signal lights for emergency vehicles, and traffic signal lights.

[0004] In the past, efforts to improve the efficiency of amber ceramics focused on increasing their density. Reducing porosity reduces the proportion of scattering from pores. However, since the crystal structure of (Sr,Ba)₂Si₅N₈:Eu is not cubic, grain boundary scattering caused by birefringence always exists. Furthermore, it is difficult to achieve a Ba₁Si₇N₈ crystal structure with a high density of 10⁻⁴N₈. 10 -To completely eliminate the secondary phase, since variation at the secondary phases is always present. Therefore, there is a limit to improving efficiency by reducing porosity, as variation at the grain boundary and secondary phases cannot be avoided.

[0005] US patent US 8 957 493 B1 discloses a light-emitting diode (LED) arrangement comprising a layer of a wavelength converter and a filter layer.

[0006] Oh et al., Optics Express 2010,18(11), 11063-11072 reveal an amber fluorescent LED that includes a filter layer. SUMMARY

[0007] The object of the present invention is to eliminate the disadvantages of the prior art.

[0008] Another object of the present invention is to provide a wavelength converter that could be used for LED applications.

[0009] Another object of the present invention is to provide a method for manufacturing a wavelength converter and for providing a light-emitting device.

[0010] It is also an object of the present invention to provide a wavelength converter and a light-emitting device which are produced by a method according to the present invention.

[0011] According to an object of the present invention, a wavelength converter is provided, comprising: a phosphor layer and a filter layer wherein the filter layer is directly attached to the phosphor layer and wherein the wavelength converter has a total thickness between about 20 µm and about 80 µm and wherein the filter layer comprises at least two different metal oxides selected from the group consisting of SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3.

[0012] According to a further aspect of the present invention, a light-emitting device is provided, comprising: an LED chip, and comprising a wavelength converter: a phosphor layer and a filter layer wherein the filter layer is attached directly to the phosphor layer and wherein the wavelength converter has a total thickness between about 20 µm and about 80 µm.

[0013] According to a further subject matter of the present invention, a method for manufacturing a wavelength converter is provided, comprising the following steps: providing a glass substrate or a sapphire wafer, Coating the glass substrate or sapphire wafer with a filter layer comprising various metal oxides to produce a coated glass substrate or a coated sapphire wafer, Providing a phosphor material, and attaching the coated glass substrate or coated sapphire wafer to the phosphor material, thereby providing a wavelength converter, wherein the filter layer is attached directly to the phosphor layer and wherein the wavelength converter has a total thickness between about 20 µm and about 80 µm and wherein the metal oxides are selected from the group consisting of SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The invention is explained in more detail below with reference to the exemplary embodiments and the accompanying figures. The figures are sketches and are not to scale. Fig. Figure 1 shows a SEM image of the (Sr,Ba)2Si5N8:Eu amber ceramic (Sr,Ba)2Si5N8:Eu, Fig. Figure 2 shows the lumen values ​​of (Sr,Ba)2Si5N8:Eu amber ceramic LEDs vs. ceramic plate thickness; Fig. Figure 3 shows the color of (Sr,Ba)2Si5N8:Eu-Amber ceramic LEDs vs. ceramic thickness; Fig. Figure 4 shows the color of (Sr,Ba)2Si5N8:Eu-Amber ceramic plates of different thicknesses, measured with an OSRAM tester; Fig. Figure 5 shows the reflectance of a filter layer according to Table 1 and the emission of an amber plate before and after coating; Fig. Figure 6 shows the color of (Sr,Ba)2Si5N8:Eu-Amber ceramic plates of different thicknesses before and after coating, measured with the OSRAM tester; Fig. Figure 7 shows the color of (Sr,Ba)2Si5N8:Eu-coated amber ceramic tiles in an LED package; Fig. Figure 8 shows the lumen values ​​of coated amber ceramic tiles in an LED package; Fig. Figure 9 shows a SEM image of a cross-section of a coating on an amber ceramic plate; Fig. Figure 10 shows the color of coated amber ceramic plates with unpolished and polished surfaces, tested with OSRAM tester measurement; Fig. Figure 11 shows a schematic view of a filter layer on a transparent layer on an amber ceramic plate; Fig. Figure 12 shows a schematic view of a filter layer on a transparent layer on an amber ceramic in an LED package; Fig. Figure 13 shows an exemplary method for manufacturing a wavelength converter; Fig. Figure 14 shows an exemplary method for manufacturing a light-emitting device arrangement; Fig. Figure 15 shows a schematic representation of light and heat transfer in a thick ceramic; Fig. Figure 16 shows a schematic representation of light and heat transfer in a thin ceramic material; Fig. Figure 17 shows the spectral reflection properties of the filter layer at different angles of incidence; Fig. Figure 18 shows the color of (Sr,Ba)2Si5N8:Eu amber ceramic LEDs from different viewing angles for (1) a thin ceramic layer with a filter layer and (2) a thick ceramic layer without a filter; and Fig. Figure 19 shows exemplary embodiments of wavelength converters. DETAILED DESCRIPTION OF THE EXPLANATORY EXECUTION FORMS

[0015] For a better understanding of the present invention, together with other and further aims, advantages and possibilities thereof, reference is made to the following disclosure and the attached claims in conjunction with the drawings described above.

[0016] References to the color of the phosphor, LED, or conversion material generally refer to its emission color, unless otherwise specified. Thus, a blue LED emits blue light, a yellow phosphor emits yellow light, and so on.

[0017] The present invention relates to a wavelength converter comprising: a phosphor layer and a filter layer wherein the filter layer is attached directly to the phosphor layer and wherein the wavelength converter has a total thickness between 20 µm and 80 µm wherein the filter layer comprises at least two different metal oxides selected from the group consisting of SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3.

[0018] As used herein, a wavelength converter is a solid structure that converts at least some of the light of a specific first wavelength into light of a specific second wavelength. In one embodiment, the light of a specific first wavelength is blue light. Structures capable of generating light of a first wavelength include, for example, InGaN or GaN chips or solid-state laser diodes.

[0019] A phosphor is a material that converts light of a specific first wavelength into light of a specific second wavelength.

[0020] According to the present invention, the wavelength converter comprises a phosphor layer. The phosphor layer can consist of the phosphor itself, or alternatively, it can comprise a host material in which the phosphor is embedded. In the latter case, the phosphor can be embedded in a ceramic or glass host material. Preferably, the host materials are transparent to the incident light of a specific first wavelength. The phosphor layer can also be a ceramic phosphor layer.

[0021] The phosphor layer (e.g. the ceramic phosphor layer) can have a smooth, preferably a polished surface.

[0022] Examples of phosphors include garnets, oxynitridosilicates, perovskites, quantum dots, silicates or combinations thereof, each doped with at least one suitable element.

[0023] In one embodiment, the phosphor is selected from the group consisting of (Ba,Sr)2Si5N g :Eu 2+ , Ca-α-SiAlON:Eu 2+ , YAG:Ce+CaAlSiN3:Eu, (Ca,Sr)AlSiN3:Eu 2+ , (Sr,Ca)Al2Si2N6:Eu 2+ , (Ba,Sr,Ca)2Si5N8:Eu 2+ and Sr(LiAl3N4):Eu 2+ .

[0024] The phosphor (e.g., the phosphor mentioned herein) can be mixed with a ceramic host material selected from the group consisting of undoped (Ba,Sr)2Si5N8:Eu 2+ , Ca-α-SiAlON or AlN or a glass host material consisting of low melting point glass, borate silicate or phosphate glass.

[0025] In preferred embodiments, the phosphor layer is a layer of (Ba,Sr,Ca)2Si5N8:Eu2+ , or (Ba,Sr)2Si5N8:Eu 2+ , i.e., a layer of amber ceramic. In another preferred embodiment, the phosphor layer is (Ba,Sr)2Si5N8:Eu 2+ .

[0026] In an alternative embodiment, the phosphor layer comprises at least two different phosphors, at least three different phosphors, or at least four different phosphors.

[0027] In one embodiment, the specified second wavelength, i.e., the dominant wavelength resulting from the conversion of the specified first wavelength, is approximately 590 nm. Phosphors that could convert the light to this wavelength include, for example, (Ba,Sr)₂Si₅N₂. g :Eu 2+ , Ca-α-SiAlON:Eu 2+ and YAG:Ce+CaAlSiN3:Eu. The phosphors can be present as a ceramic layer, or they can be present as particles in a host material, such as a transparent ceramic, glass or silicone.

[0028] In an alternative embodiment, the specified second wavelength, i.e., the wavelength obtained from the conversion of the specified first wavelength, is approximately 610 nm to approximately 630 nm. Phosphors that could convert the light to this wavelength include, for example, (Ca,Sr)AlSiN3:Eu. 2+ , (Sr,Ca)Al2Si2N6:Eu 2+ , (Ba,Sr,Ca)2Si5N8:Eu 2+ , Sr(LiAl3N4):Eu 2+ The phosphors can be present as a ceramic layer, or they can be present as particles in a host material, such as a transparent ceramic, glass, or silicone.

[0029] In an alternative embodiment, the specified second wavelength, i.e., the wavelength obtained from the conversion of the specified first wavelength, is greater than approximately 700 nm. Phosphors that could convert the light to this wavelength include, for example, chromium. 3+4+ -, Ni 2+-, Bi-, Yb-, Tm-, Er- etc., doped host crystals and glasses (e.g. La3Ga5GeO 14 , Ga2O3, Gd3Ga3Sc2O 12 , Mg2SiO4, etc.). The phosphors can be present as particles in a host material, such as a transparent ceramic, glass or silicone.

[0030] The phosphor layer preferably has a shape-like structure. The thickness of the phosphor layer, i.e., the length of the phosphor layer through which the light passes at a 90° angle to the emitting source surface of the light of the specific first wavelength, is, for example, between 420 and 465 nm, preferably between 445 and 455 nm.

[0031] In one embodiment, more than one phosphor layer is present, e.g., 2 layers, 3 layers or more layers are present.

[0032] The wavelength converter further includes a filter layer on its top surface. This filter layer reflects unabsorbed excitation light of a specific first wavelength, such as that emitted by an LED chip. The phosphor layer absorbs at least a portion of the light of the specific first wavelength and converts it to a specific second wavelength, while the filter layer reflects the unabsorbed light of the specific first wavelength, allowing the light of the specific second wavelength to pass through.

[0033] The filter layer is attached directly to the phosphor layer. "Directly attached" in the context of the present invention means that at least one contact point exists between the phosphor layer and the filter layer. In a preferred embodiment, at least one surface of the phosphor layer is covered with the filter layer.

[0034] The filter layer of the present invention can be a multilayer of alternative oxides. The filter can be produced by vapor or sputter deposition of these oxide layers onto a substrate. The substrate can be a phosphor layer, e.g., in the form of a ceramic material. In this case, preferably no adhesive is present between the phosphor layer and the filter layer. Alternatively, the substrate can also be a thin glass or sapphire layer. In this case, the coated glass (or sapphire) is the filter layer. The filter layer is preferably bonded to the phosphor layer.

[0035] In one embodiment, the filter layer comprises at least two metal oxides. The metal oxides of the filter layer may be present in a single layer. In an alternative aspect of this embodiment, the filter layer comprises multiple sublayers. Each of the sublayers may comprise at least one metal oxide.

[0036] The filter layer could be a dichroic filter. A dichroic filter, thin-film filter, or interference filter is a very precise color filter used to selectively transmit light of a small color range while reflecting other colors.

[0037] In a dichroic mirror or filter, alternating layers of optical coatings with different refractive indices are built up on a glass substrate. The interfaces between the layers with different refractive indices produce phase-shifted reflections that selectively amplify certain wavelengths of light and superimpose others. The layers are typically deposited by vacuum deposition. By controlling the thickness and number of layers, the wavelength of the filter's passband can be tuned and made as wide or narrow as desired. Because unwanted wavelengths are reflected and not absorbed, dichroic filters do not absorb this unwanted energy during operation and therefore do not get nearly as hot as the equivalent conventional filter (which attempts to absorb all energy except that in the passband).

[0038] The filter layer can, for example, comprise two sublayers, each comprising a different metal oxide. Preferably, the metal oxides have different refractive indices. In an alternative embodiment, the filter layer comprises three or more sublayers, each comprising a different or the same metal oxide, wherein sublayers of the same metal oxide are preferably not adjacent to one another. Therefore, the filter layer can comprise n sublayers and up to n different metal oxides. In a preferred embodiment, the filter comprises two metal oxides, one with a high refractive index and one with a low refractive index.

[0039] In one embodiment, the filter layer comprises 13 to 19 sublayers. In a preferred embodiment, the filter layer comprises 15 to 18 sublayers. In a more preferred embodiment, the filter layer comprises 16 or 17 sublayers. In a further preferred embodiment, the filter layer comprises 17 sublayers.

[0040] The metal oxides of the filter layer can be selected from SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3. Preferred metal oxide pairs are Al2O3-TiO2 or SiO2-Nb2O5.

[0041] Dichroic filters typically require two oxides with contrasting refractive indices, one with a high refractive index (H) and the other with a low refractive index (L). The filter preferably comprises alternating H and L layers of varying thicknesses, such as H, L, H, L, H, L, H, L, etc.

[0042] In one embodiment, the filter layer comprises 17 sublayers and two different metal oxides, such as alternating sublayers of Al2O3 and TiO2.

[0043] The filter layer preferably has a shape-like structure. The thickness of the filter layer, i.e., the length of the filter layer through which the light passes at a 90° angle to the emitting source surface, is, for example, between 420 and 465 nm, preferably 445 and 455 nm, for light of the specific first wavelength.

[0044] The sublayers of the filter layer can each have a thickness between approximately 20 nm and approximately 150 nm. In one embodiment, the sublayers each have a thickness between approximately 30 nm and approximately 40 nm.

[0045] The thickness of the filter layer is preferably related to the wavelength λ. The thickness is a multiple of 1 / 2λ. The present invention aims to achieve high reflectance at wavelengths below the exclusion wavelength, such as below 535 nm, in the blue excitation light and high transmittance above the exclusion wavelength in the amber phosphor emission region.

[0046] The wavelength converter can further comprise an absorption layer above the filter. The absorption layer preferably absorbs light of wavelengths that are intended to pass through the filter layer to be emitted.

[0047] Examples of absorption layers include layers of ion-doped color filter glasses, including MoS2-colored glasses, Ce-doped gallium-gadolinium-YAG, or are selected from semiconductor materials such as GaP, AlP, AlAs, CdSe, CdS in the form of thin films or nanoparticles.

[0048] The absorption layer is preferably attached to the filter layer. The absorption layer can be attached to the filter layer with an adhesive or by natural absorption forces.

[0049] The filter layer preferably has a shaped structure. The thickness of the filter layer, i.e., the length of the filter layer through which the light passes at a 90° angle to the emitting source surface of the light of the specific first wavelength, is, for example, between approximately 420 nm and approximately 465 nm, preferably between approximately 445 nm and 455 nm.

[0050] The wavelength converter has a total thickness of between approximately 20 µm and approximately 80 µm. In one embodiment, the wavelength converter has a thickness of between approximately 40 µm and approximately 70 µm. In a preferred embodiment, the wavelength converter has a thickness of between approximately 40 µm and approximately 50 µm. The thickness of the wavelength converter is the length of the wavelength converter through which the light passes at a 90° angle to the emitting source surface of the light of the specified first wavelength.

[0051] Another object of the present invention is to provide a light-emitting device arrangement comprising: an LED chip, and a wavelength converter, comprising: a phosphor layer, and a filter layer wherein the filter layer is attached directly to the phosphor layer and wherein the wavelength converter has a total thickness between about 20 µm and about 80 µm and wherein the filter layer comprises at least two different metal oxides selected from the group consisting of SiO2, Al2O3, TiO2, Nb2O3, Ta2O3, HfO2 and Y2O3.

[0052] The LED chip preferably emits blue light. In an alternative embodiment, the LED chip emits UV light. Examples of LED chips are GaN / InGaN-based semiconductor materials.

[0053] The wavelength converter, the phosphor layer and the filter layer each correspond to the devices described above.

[0054] It is an object of the present invention to provide a method for manufacturing a wavelength converter, comprising the steps of: Providing a glass substrate or a sapphire wafer, Coating the glass substrate or sapphire wafer with a filter layer comprising various metal oxides to produce a coated glass substrate or a coated sapphire wafer, providing a phosphor, and Attaching the coated glass substrate or coated sapphire wafer to the phosphor, thereby providing a wavelength converter, wherein the filter layer is applied directly to the phosphor layer and wherein the wavelength converter has a total thickness between about 20 µm and about 80 µm and wherein the metal oxides are selected from the group consisting of SiO2, Al2O3, TiO2, Nb2O3, Ta2O3, HfO2 and Y2O3.

[0055] In one step of the process for manufacturing a wavelength converter, a glass substrate or a sapphire wafer is provided. The glass substrate or the sapphire wafer is preferably transparent and thus particularly transparent to wavelengths that are to be emitted from the wavelength converter.

[0056] The glass substrate or sapphire wafer can have a thickness of approximately 40 to approximately 200 µm. In one embodiment, the glass substrate or sapphire wafer can have a thickness between approximately 40 and approximately 100 µm.

[0057] In a further step, the glass substrate or sapphire wafer is coated with at least two layers of metal oxides to provide a coated glass substrate or a coated sapphire wafer. The coating is preferably achieved by depositing a pair of Al₂O₃-TiO₂ or SiO₂-Nb₂O₃ oxides; however, other metal oxides can also be deposited on the glass substrate or the sapphire wafer.

[0058] In one embodiment, the coating process is carried out stepwise. Thus, the first layer of at least one metal oxide is applied to the glass substrate or sapphire wafer. In a subsequent step, a second layer of at least one metal oxide is applied to the first layer of at least one metal oxide on the glass. Further layers, if any, are applied accordingly. An optional drying step is included between the coating steps or at least after the final coating step. The coating can be carried out by vapor deposition or sputtering.

[0059] In one embodiment of the present invention, the layers of metal oxides correspond to the sublayers of the filter layer mentioned herein, and the sum of all layers of metal oxides applied to the glass substrate or the sapphire wafer corresponds to the filter layer mentioned herein.

[0060] In one embodiment, the metal oxides are selected from SiO2, Al2O3, TiO2, Nb2O5, Ta2O3, HfO2 and Y2O3. Preferred metal oxides are oxide pairs of Al2O3-TiO2 or SiO2-Nb2O5.

[0061] In one embodiment, 17 layers of metal oxides are applied to the glass substrate or the sapphire wafer, and the metal oxides are Al2O3 and TiO2.

[0062] In a further step, a phosphor is provided. Examples of phosphors are garnets, oxynitride silicates, perovskites, quantum dots, silicates, or combinations thereof, each doped with at least one suitable element.

[0063] In one embodiment, the phosphor is selected from the group consisting of (Ba,Sr)2Si5N8:Eu 2+ , Ca-α-SiAlON:Eu 2+ , YAG:Ce+CaAlSiN3:Eu, (Ca,Sr)AlSiN3:Eu 2+ , (Sr,Ca)Al2Si2N6:Eu 2+ , (Ba,Sr,Ca)2Si5N8:Eu 2+ and Sr(LiAl3N4):Eu 2+ .

[0064] The phosphor (e.g., the phosphor mentioned herein) can be mixed with a ceramic host material selected from the group consisting of undoped (Ba,Sr)2Si5N8:Eu 2+ , Ca-α-SiAlON or AlN or a glass host material consisting of low melting point glass, borate silicate or phosphate glass.

[0065] In preferred embodiments, the phosphor material is a layer of (Ba,Sr)2Si5N8:Eu 2+ or (Ba,Sr)2Si5N8:Eu 2+ , i.e., a layer of amber ceramic. In another preferred embodiment, the phosphor is (Ba,Sr)2Si5N8:Eu 2+ .

[0066] In an alternative embodiment, the phosphor material comprises at least two different phosphors, at least three different phosphors, or at least four different phosphors.

[0067] In one embodiment, the specified second wavelength, i.e., the dominant wavelength resulting from the conversion of the specified first wavelength, is approximately 590 nm. Phosphors capable of converting light to this wavelength include, for example, (Ba,Sr)₂Si₅N₈:Eu. 2+ , Ca-α-SiAlON:Eu 2+ and YAG:Ce+CaAlSiN3:Eu. The phosphors can be present as a ceramic layer or as particles in a host material, such as transparent ceramic, glass or silicone.

[0068] In an alternative embodiment, the specified second wavelength, i.e., the wavelength obtained from the conversion of the specified first wavelength, is approximately 610 nm to approximately 630 nm. Phosphors capable of converting light to this wavelength include, for example, (Ca,Sr)AlSiN3:Eu. 2+ , (Sr,Ca)Al2Si2N6:Eu 2+ , (Ba,Sr,Ca)2Si5N8:Eu 2+ , Sr(LiAl3N4):Eu 2+The phosphors can be present as a ceramic layer or as particles in a host material, such as a transparent ceramic, glass or silicone.

[0069] In an alternative embodiment, the specified second wavelength, i.e., the wavelength obtained from the conversion of the specified first wavelength, is greater than approximately 700 nm. Phosphors capable of converting light to this wavelength include, for example, C. r 3+ / 4+ , Ni 2+ , Bi, Yb, Tm, Er etc. doped host crystals and glasses (e.g. La3Ga5GeO 14 , Ga2O3, Gd3Ga3Sc2O 12 , Mg2SiO4, etc.). The phosphors can be present as particles in a host material, such as a transparent ceramic, glass or silicone.

[0070] The coated glass substrate or coated sapphire wafer is attached to the phosphor material to provide a wavelength converter. In one embodiment, the coated glass substrate or coated sapphire wafer is attached to the phosphor material by laminating it with an adhesive.

[0071] The adhesive can be transparent epoxy, silicone, or polysiloxane.

[0072] In a preferred embodiment, the phosphor is attached to the metal oxide layer(s), and the glass substrate or sapphire wafer is located opposite the phosphor. In an alternative embodiment, the phosphor layer is attached to the glass substrate or sapphire wafer, and the filter layer is located opposite the phosphor layer.

[0073] In another embodiment, an adsorption layer, as mentioned herein, is attached to the filter layer.

[0074] In one embodiment, the wavelength converter is divided into smaller pieces. Typical sizes for a wavelength converter are 0.75 mm × 0.75 mm, 1 mm × 1 mm, or 2 mm. 2 In a preferred embodiment, the wavelength converter has a size of 1 mm × 1 mm.

[0075] Another subject matter is to provide a method for manufacturing a light-emitting device arrangement, comprising: Providing an LED chip that is optionally attached to a leadframe, Installation of a wavelength converter including: a phosphor layer and a filter layer on the LED chip, wherein the filter layer is attached directly to the phosphor layer and wherein the wavelength converter has a total thickness of between about 20 µm and about 80 µm.

[0076] The LED chip, the phosphor layer and the filter layer each correspond to the devices described herein.

[0077] In one embodiment, the wavelength converter is attached to the LED chip using a silicone adhesive.

[0078] Another object is to provide a light-emitting device manufactured according to a method of the present invention.

[0079] In one embodiment of the present invention, a wavelength converter of the present invention is used in LED packages for industrial and automotive lighting.

[0080] A typical microstructure of (Sr,Ba)2Si5N8:Eu-amber ceramic is found in Fig. Figure 1 shows the bright matrix phase (Sr,Ba)2Si5N8. The darker phases are Ba1Si7Ni. 10 The ceramics also contain some pores. Within the amber ceramics, there can be quite strong scattering. The first source of scattering is grain boundary scattering, since (Sr,Ba)₂Si₅N₈ is not a cubic structure. The second source of scattering comes from the Ba₁Si₇Ni. 10 -Secondary phases. The third scattering comes from the pores due to a large refractive index contrast between the pore and the matrix.

[0081] Due to the significant scattering often present in amber ceramic material, the total scattering depends on the thickness of the amber ceramic material. The thicker the samples, the greater the scattering. Fig. Figure 2 shows the lumen values ​​at a drive current of 350 mA for LEDs using amber ceramic chip converters of varying thicknesses. Ld=447 nm means that the LED chip emits blue light with a dominant wavelength of 447 nm. W / O casting means that the LED chip and converter are not encapsulated in white silicon. It is clearly visible that the LED lumens decrease with increasing thickness of the amber ceramic. This is due to increased scattering and a reduced package efficiency.

[0082] It would seem natural that a thinner amber ceramic would be preferred due to its higher package lumens. But according to the in Fig. In the three shown colors of amber ceramic LEDs of varying thicknesses, the color of the thinnest amber ceramic LEDs falls outside the required color specification. The larger dashed box represents the ECE (Economic Commission for Europe) amber color requirement. Although thinner amber ceramics yield higher package lumens, they cannot absorb all blue light and therefore have more residual blue light. More residual blue light leads to a decrease in the color Cx. The emission color gradually shifts towards higher emission-dominant wavelengths with increasing thickness. This is due to the self-absorption of thicker samples.

[0083] The current standard thickness of amber ceramics in wavelength converters is approximately 120 µm. This thickness would guarantee that the ceramic is thick enough to absorb most of the light of a specific first wavelength, such as blue light. The plate thickness was reduced to approximately 90 and 70 µm. The color and conversion efficiency (CE) were measured using an in-house pinhole setup: the OSRAM Tester. Stabilized and constant blue light passes through a pinhole on which the plate sample sits. The forward-transmitted residual blue light and the emitted amber light were collected by a small integrating sphere above the sample. The color and conversion efficiency (CE) (forward-transmitted lumens divided by the incident blue powder, lm / W_b) were measured.

[0084] Fig. Figure 4 shows the color distribution of amber ceramic plates with thicknesses of 120, 90, and 70 µm. For a standard thickness of 120 µm, the plates have an average CE of 91.4 Im / W. As the thickness decreases to 90 and 70 µm, the CE increases to 96.4 and 98 Im / W, respectively.

[0085] A wavelength converter with the filter layer according to the present invention was manufactured. The phosphor material was a layer of amber ceramic materials. The filter consisted of 17 sublayers of alternating low- and high-refractive-index materials, Al₂O₃ and TiO₂. (Table 1: Filter structure). Teilschicht Nr. Filterschicht Dicke [nm] 1 Al2O3 37 2 TiO2 43 3 Al2O3 63 4 TiO2 50 5 Al2O3 62 6 TiO2 51 7 Al2O3 66 8 TiO2 50 9 Al2O3 68 10 TiO2 49 11 Al2O3 65 12 TiO2 51 13 Al2O3 68 14 TiO2 48 15 Al2O3 54 16 TiO2 53 17 Al2O3 127 Luft

[0086] A reflection curve simulated from the filter setup in Table 1 is shown in Fig. Figure 5 shows a high reflectance between 410 and 500 nm. Above 500 nm, the reflectance drops rapidly, with an exclusion wavelength at approximately 530 nm. Such a coating can be applied to amber ceramic plates by electron beam evaporation, sputtering, or other coating processes. An amber-colored plate was measured with the OSRAM tester before and after coating. The measurement results are compared with a simulated reflection curve of the coating in Figure 5. Fig. 5 compared. After coating, the blue residual light at 450 nm is greatly reduced, while the amber emission at 600 nm is slightly increased.

[0087] Fig. Figure 6 compares the color distribution of amber ceramic plates with thicknesses of 120, 90, and 70 µm before and after coating. The Cx value of all coated plates increases. The thinner the coated plates, the greater the increase in their Cx value. The CE value of the coated plates is approximately 1% higher than before coating.

[0088] Coated plates were arranged together with uncoated amber plates as a reference in an LED package. The emission color of the coated amber plates in the package ( Fig. 7) is the color that is measured with the Osram tester in Fig. 6 was measured, very similar. The packet lumens at 700 mA for coated amber plates are 5-18% higher than uncoated reference plates ( Fig. 8).

[0089] In some embodiments, the amber ceramic surface treatment is another aspect of the coating process. Fig. Figure 9 shows a SEM image of a cross-section of a coated amber ceramic. The ceramic surface, as if ground, is not very smooth. This surface imperfection can negatively affect the coating in two ways. First, it can reduce the coating quality. Second, it can introduce scattering, which affects the angle of incidence of light on the coating. The reflectance of the coating can depend on the angle of incidence of the light. As the angle of incidence increases, the reflectance curve shifts. Fig. Moving the lens 5 degrees to the left decreases the exclusion wavelength. Therefore, scattering caused by surface imperfections can alter the reflectance / transmittance. For coating purposes, a polished amber ceramic surface is preferably used.

[0090] The amber platelets with thicknesses of 70, 90, and 120 µm were polished down to 1 µm using a diamond slurry. Subsequently, the polished platelets and the platelets that had only been ground were coated with the layers according to Table 2. Table 2 Teilschicht Nr. Filterschicht Dicke [nm] 1 Al2O3 32,7 2 TiO2 53,1 3 Al2O3 55 4 TiO2 51,3 5 Al2O3 67 6 TiO2 53,9 7 Al2O3 60,9 8 TiO2 56 9 Al2O3 68,1 10 TiO2 46,4 11 Al2O3 71,1 12 TiO2 59,6 13 Al2O3 48,9 14 TiO2 52,4 15 Al2O3 63 16 TiO2 57,1 17 Al2O3 128,8 Luft

[0091] The coated polished and unpolished plates were measured with the OSRAM tester ( Fig. 10) The color of all polished plates is more saturated than that of the unpolished plates, as indicated by an increase in Cx, meaning there is less residual blue in coated polished plates. Their CE is also 1-2% higher.

[0092] Another embodiment is a stack of a thin arrangement consisting of a phosphor layer and a filter layer with a further transparent layer, preferably glass, Al2O3 or silicone ( Fig. 11) Between the transparent layer 5 and the phosphor layer 2 is the filter layer 3. The filter layer can first be applied to the transparent layer 5 using high-volume processes and then bonded to the phosphor layer 2 (e.g. (Sr,Ba)2Si5N8 amber ceramic) by means of transparent epoxy, silicone or polysiloxane, water glass or a low-melting-point glass.

[0093] The advantage of this embodiment is that a transparent layer, such as glass, can have a much smoother surface than ceramic materials. Therefore, the filter layer on such a phosphor layer can be of higher quality. Since thinner amber ceramic with lower scattering is used in the disclosure, a potential problem is that the height of the ceramic is lower than the highest point of the bond wire ( Fig. 12) The highest section of the wire cannot be covered by casting protection material, such as silicone. Thus, a further advantage of this embodiment is that the overall thickness of the hybrid can be adjusted to be greater than the bond wire, so that all the bond wires can be protected by sidewall potting in the package ( Fig. 12).

[0094] Fig. Figure 13 shows an exemplary process for manufacturing a wavelength converter. In a first step, a filter layer 3 is applied to a glass substrate or a sapphire wafer 8. The phosphor layer 2 is attached to the filter layer with an adhesive 9. This results in a so-called multilayer stack. In a subsequent step, the multilayer stack is cut into smaller pieces.

[0095] Fig. Figure 14 shows an exemplary method for manufacturing a light-emitting device assembly 6. In a first step, the wavelength converter 1 is attached to the LED chip 7, which is mounted on a leadframe 10. A bond wire 11 is attached to the LED chip 7. In a further step, the assembly is molded using a molding tool 12 in a molding step, with a protective silicone potting 13 in place. After the molding step, a light-emitting device assembly 6 is obtained.

[0096] Fig. 15 shows an exemplary thick ceramic, while Fig. Figure 16 shows a thin ceramic according to the invention. The conversion of blue light into light of longer wavelengths in the converter ceramic generates heat due to Stokes displacement losses. This leads to a temperature increase in the ceramic element. The thermal resistance of the converter element, and thus the maximum temperature, increases with thickness. The conversion efficiency decreases with temperature, and degradation increases. Therefore, reducing the thickness of the ceramic improves the performance of the converter LED, especially in high-power applications and current densities >1 A / mm². 2 Therefore, a thin ceramic layer (d < 70 µm) with a coating is better than a thick layer. In summary, R th_thick > R th_thin to T thick > T thin .

[0097] Fig. Figure 17 shows the reflection properties of a coating. One problem is that the reflection band of a dielectric coating shifts in wavelength with the angle of incidence. 100% reflection of the wide blue LED (FWHM ~ 25 nm) cannot be guaranteed for all angles of incidence. Therefore, the color is less saturated, for example, at high angles of incidence. A possible solution is to add a wavelength-selective absorption layer to the filter layer, which leads to the absorption of blue light and thus the transmission of light of a longer wavelength. The majority of the unabsorbed blue light (e.g., >90%) is reflected by the filter layer, and the remainder is absorbed by the blue filter.The filter layer band and the blue LED should be matched so that perpendicular incidence is best reflected and higher angles are partially transmitted, since the optical path length in the absorption layer is longer for higher angles of incidence.

[0098] Fig. Figure 18 shows the color of a ceramic-coated LED from different viewing angles. 0° represents observation along the optical axis, larger angles represent oblique observation. While the color shift between direct and oblique observation is small for a thick ceramic layer without a mirror (2), it can vary considerably for a thin ceramic layer with a dielectric filter (1). In this case, blocking light from oblique angles, additional mixing optics, or, as described, an additional absorbing layer above the reflecting mirror may be necessary.

[0099] Fig.Figure 19 shows various embodiments of wavelength converters 1. An absorption layer 4 could be applied directly to the filter layer 3 or to the bottom or top surface of the glass substrate or sapphire wafer 8. Another possibility is to coat a blue filter glass with the filter layer 3. Materials for the absorption layers can include: ion-doped glasses (Schott filter glasses), converter materials with high activator concentration and high quenching, or, especially for thin coatings, semiconductor materials with a band gap larger than the emission (e.g., GaP or similar for yellow).

[0100] The methods and equipment described herein offer the advantage of higher effectiveness with thinner ceramics, while simultaneously ensuring that their color meets the color requirements.

[0101] In general, thick layers in wavelength converters are often ineffective due to scattering, but often exhibit high color saturation. The thinner the wavelength converters, the less scattering often occurs, resulting in higher efficiency but lower color saturation. The wavelength converters of the present invention exhibit low scattering, low back reflection, high efficiency, and good saturation.

[0102] While it has been shown and described what are currently considered preferred embodiments of the invention, it is obvious to the person skilled in the art that various changes and modifications can be made herein without deviating from the scope of the invention as defined by the attached claims.

Claims

[1] Wavelength converter comprising: a phosphor layer; and a filter layer where the filter layer is attached directly to the phosphor layer, wherein the wavelength converter has a total thickness between 20 µm and 80 µm, wherein the filter layer comprises at least two different metal oxides selected from the group consisting of SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3. [2] Wavelength converter according to claim 1, wherein a phosphor of the phosphor layer is selected from the group consisting of (Ba,Sr)2Si5N g :Eu 2+ , Ca-α-SiAlON:Eu 2+ , YAG:Ce+CaAlSiN3:Eu, (Ca,Sr)AlSiN S :Eu 2+ , (Sr,Ca)Al2Si2N6:Eu 2+ , (Ba,Sr,Ca)2Si5N8:Eu 2+ and Sr(LiAl3N4):Eu 2+ . [3] Wavelength converter according to claim 1, further comprising an absorption layer. [4] Wavelength converter according to claim 3, wherein the absorption layer is selected from ion-doped color filter glasses comprising MoS2-colored glasses, Ce-doped gallium-gadolinium-YAG, or is selected from semiconductor materials. [5] Wavelength converter according to claim 4, wherein the semiconductor materials comprise GaP, AlP, AlAs, CdSe or CdS in the form of thin films or in the form of nanoparticles. [6] Light-emitting device arrangement comprising: an LED chip; and comprising a wavelength converter: a phosphor layer; and a filter layer the filter layer is attached directly to the phosphor layer, and wherein the wavelength converter has a total thickness between 20 µm and 80 µm, and wherein the filter layer comprises at least two different metal oxides selected from the group consisting of SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3. [7] Method for manufacturing a wavelength converter, the method comprising: Providing a glass substrate or a sapphire wafer, Coating the glass substrate or sapphire wafer with a filter layer comprising various metal oxides to produce a coated glass substrate or a coated sapphire wafer, providing a phosphor, and Attaching the coated glass substrate or the coated sapphire wafer to the phosphor, providing a wavelength converter that includes a phosphor layer, wherein the filter layer is attached directly to the phosphor layer, wherein the wavelength converter has a total thickness between 20 µm and 80 µm, and the metal oxides are selected from the group consisting of SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3. [8] Method according to claim 7, wherein the phosphor material is selected from the group consisting of (Ba,Sr)2Si5N g :Eu 2+ , Ca-α-SiAlON:Eu 2+ , YAG:Ce+CaAlSiN:Eu, (Ca,Sr)AlSiN3:Eu 2+ , (Sr,Ca)Al2Si2N6:Eu 2+ , (Ba,Sr,Ca)2Si5N8:Eu 2+ and Sr(LiAl3N4):Eu 2 . [9] Method according to claim 7, wherein the application of the coated glass substrate or the coated sapphire wafer to the phosphor material comprises laminating the coated glass substrate or the coated sapphire wafer to the phosphor material with an adhesive. [10] Method according to claim 7, furthermore applying an absorption layer to the wavelength converter. [11] The method according to claim 7 further comprising the comminution of the wavelength converter. [12] Wavelength converter manufactured according to the method of claim 7.

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