Dielectric film coatings for full conversion ceramic wafers

Abstract

The invention relates to a wavelength converter, comprising: a phosphor layer and a filter layer, wherein the filter layer is directly attached to the phosphor layer, and wherein the total thickness of the wavelength converter is 20 μm to 80 μm. In addition, the invention relates to a light emitting device assembly and a method for preparing a wavelength converter and a method for preparing a light emitting device assembly.

Description

Technical Field

[0001] The present invention relates to a wavelength converter, a light emitting device assembly and a method for preparing the wavelength converter and the light emitting device. Background Art

[0002] There are several implementations of phosphor wavelength converters in the prior art. Typically, a ceramic phosphor material is used to convert light of a specific wavelength to a specific other wavelength. However, some ceramic phosphor materials exhibit scattering.

[0003] For example, an amber ceramic with the composition (Sr,Ba)2Si5N8:Eu is used in full conversion LED applications, where the blue light from the blue LED die is completely or almost completely absorbed by the amber ceramic plate converter on top of the LED die and re-emitted as amber light at a longer wavelength. Full conversion amber LEDs have a wide range of applications, such as automotive turn signals and tail lights, emergency vehicle signal lights, and traffic lights.

[0004] Previously, efforts to improve the efficiency of amber ceramics have focused on increasing the densification of amber ceramics. By reducing the porosity, the portion of scattering from the pores is reduced. However, since the crystal structure of (Sr,Ba)2Si5N8:Eu is not cubic, there is always grain boundary scattering caused by birefringence. In addition, since the crystal structure of Ba1Si7N 10 Scattering by the second phase always exists, so it is difficult to completely remove the second phase. Therefore, there is a limit to improving efficiency by reducing porosity because scattering from grain boundaries and the second phase cannot be avoided.

[0005] US Patent No. 8,957,493 discloses a light emitting diode (LED) assembly including a layer of a wavelength converter and a layer of a filter.

[0006] Oh et al., Optics Express 2010, 18(11), 11063-11072 discloses an amber phosphor LED including a filter layer. Summary of the invention

[0007] An 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 can be used in LED applications.

[0009] It is a further object of the present invention to provide a method for preparing a wavelength converter and for providing a light emitting device.

[0010] Another object of the present invention is to provide a wavelength converter and a light emitting device prepared by the method according to the present invention.

[0011] According to one object of the present invention, there is provided a wavelength converter, comprising:

[0012] Phosphor layer and

[0013] Filter layer,

[0014] Wherein the filter layer is directly attached to the phosphor layer, and wherein the total thickness of the wavelength converter is from about 20 μm to about 80 μm.

[0015] According to another object of the present invention, there is provided a light emitting device assembly, comprising:

[0016] LED die, and

[0017] A wavelength converter, the wavelength converter comprising:

[0018] a phosphor layer, and

[0019] Filter layer,

[0020] Wherein the filter layer is directly attached to the phosphor layer, and wherein the total thickness of the wavelength converter is from about 20 μm to about 80 μm.

[0021] According to another object of the present invention, there is provided a method for preparing a wavelength converter, the method comprising the following steps:

[0022] Provide glass substrate or sapphire wafer,

[0023] coating a glass substrate or a sapphire wafer with a filter layer comprising different metal oxides to prepare a coated glass substrate or a coated sapphire wafer,

[0024] providing a phosphor material, and

[0025] Attaching a coated glass substrate or a coated sapphire wafer to the phosphor material provides a wavelength converter,

[0026] Wherein the filter layer is directly attached to the phosphor layer, and wherein the total thickness of the wavelength converter is from about 20 μm to about 80 μm.

[0027] According to another object of the present invention, there is provided a method for preparing a light emitting device assembly, comprising:

[0028] providing an LED die, optionally attached to a lead frame,

[0029] Attaching a wavelength converter to the LED die, the wavelength converter comprising:

[0030] a phosphor layer, and

[0031] Filter layer,

[0032] Wherein the filter layer is directly attached to the phosphor layer, and wherein the total thickness of the wavelength converter is from about 20 μm to about 80 μm.

[0033] According to another object of the present invention, there is provided a wavelength converter prepared by the method according to the present invention.

[0034] According to another object of the present invention, a light-emitting device prepared by the method according to the present invention is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention is explained in more detail below based on embodiments and with reference to the associated drawings.The drawings are schematic and do not represent a true-to-scale representation.

[0036] Figure 1 The SEM image of (Sr,Ba)2Si5N8:Eu amber ceramic is shown;

[0037] Figure 2 The relationship between the lumen of the (Sr,Ba)2Si5N8:Eu amber ceramic LED and the thickness of the ceramic sheet is shown;

[0038] Figure 3 The relationship between the color of (Sr,Ba)2Si5N8:Eu amber ceramic LED and the thickness of the ceramic is shown;

[0039] Figure 4 shows the color of (Sr,Ba)2Si5N8:Eu amber ceramic sheets with various thicknesses measured by an OSRAM tester;

[0040] Figure 5 The reflectance of the filter layer according to Table 1 and the emission of the amber sheet before and after coating are shown;

[0041] Figure 6 shows the color of (Sr,Ba)2Si5N8:Eu amber ceramic sheets with various thicknesses before and after coating measured by an OSRAM tester;

[0042] Figure 7 The color of the (Sr,Ba)2Si5N8:Eu coated amber ceramic sheet in an LED package is shown;

[0043] Figure 8 The lumens of the coated amber ceramic sheet in the LED package are shown;

[0044] Fig. 9 An SEM image of a cross section of a coating on an amber ceramic sheet is shown;

[0045] Fig.10Shown is the color of a coated amber ceramic sheet having an unpolished surface and a polished surface measured and tested with an OSRAM tester;

[0046] Fig.11 A schematic diagram showing a filter layer on a transparent layer on top of an amber ceramic sheet;

[0047] Fig.12 Schematic diagram showing a filter layer on a transparent layer on top of an amber ceramic in an LED package;

[0048] Fig.13 An exemplary method for preparing a wavelength converter is shown;

[0049] Fig.14 An exemplary method for preparing a light emitting device assembly is shown;

[0050] Fig.15 Schematic diagram showing light and heat transport in thick ceramics;

[0051] Fig.16 Schematic diagram showing light and heat transport in thin ceramics;

[0052] Fig.17 shows the spectral reflectance characteristics of the filter layer at different incident angles;

[0053] Fig.18 shows the color of a (Sr,Ba)2Si5N8:Eu amber ceramic LED as seen from different viewing angles for (1) a thin ceramic layer with a filter layer and (2) a thick ceramic layer without a filter; and

[0054] Fig.19 Exemplary embodiments of wavelength converters are shown. DETAILED DESCRIPTION

[0055] For a better understanding of the present invention, together with other and further objects, advantages and features of the present invention, reference is made to the following disclosure and appended claims taken in conjunction with the above-described drawings.

[0056] Unless otherwise stated, reference to the color of a phosphor, LED, or conversion material is generally reference to its emission color. Thus, a blue LED emits blue light, a yellow phosphor emits yellow light, and so on.

[0057] The present invention relates to a wavelength converter, comprising:

[0058] a phosphor layer, and

[0059] Filter layer,

[0060] Wherein the filter layer is directly attached to the phosphor layer, and wherein the total thickness of the wavelength converter is 20 μm to 80 μm.

[0061] As used herein, a wavelength converter is a solid structure that converts at least a portion of light of a specific first wavelength into light of a specific second wavelength. In one embodiment, the light of the specific first wavelength is blue light. The structure that can generate light of the first wavelength is, for example, an InGaN or GaN chip, or a solid-state laser diode.

[0062] A phosphor is a material that converts light of a specific first wavelength into light of a specific second wavelength.

[0063] According to the invention, the wavelength converter comprises a phosphor layer. The phosphor layer may consist of a phosphor material or, alternatively, comprise a host material in which the phosphor is embedded. In the latter case, the phosphor may be embedded in a ceramic host material or a glass host material. Preferably, the host material is transparent for incident light of a specific first wavelength. The phosphor layer may also be a phosphor ceramic layer.

[0064] The phosphor layer (eg, phosphor ceramic layer) may have a smooth surface, preferably a polished surface.

[0065] Exemplary phosphors are garnets, oxynitride silicates, perovskites, quantum dots, silicates, or combinations thereof, each doped with at least one suitable element.

[0066] In one embodiment, the phosphor is selected from (Ba, Sr)2Si5N8:Eu 2+ 、Ca-α-SiAlON:Eu 2+ , YAG:Ce+CaA1SiN3:Eu, (Ca,Sr)AlSiN3:Eu 2+ 、(Sr,Ca)Al2Si2N6:Eu 2+ 、(Ba,Sr,Ca)2Si5N8:Eu 2+ and Sr(LiA13N4):Eu 2+ .

[0067] The phosphor (eg, the phosphor mentioned herein) may be selected from undoped (Ba, Sr) 2 Si 5 N 8 :Eu 2+ , Ca-α-SiAlON or AlN, or mixed with a glass host material composed of a low melting temperature glass, borosilicate glass or phosphate glass.

[0068] In a preferred embodiment, the phosphor layer is (Ba, Sr, Ca)2Si5N8:Eu 2+, or (Ba,Sr)2Si5N8:Eu 2+ In a further preferred embodiment, the phosphor layer is (Ba, Sr) 2 Si 5 N 8 :Eu 2+ .

[0069] In an alternative embodiment, the phosphor layer comprises at least two different phosphors, at least three different phosphors, or at least four different phosphors.

[0070] In one embodiment, the specific second wavelength, i.e., the dominant wavelength obtained from the conversion of the specific first wavelength, is about 590 nm. A phosphor that can convert light to this wavelength is, for example, (Ba, Sr)2Si5N8:Eu 2+ 、Ca-α-SiAlON:Eu 2+ and YAG:Ce+CaA1SiN3:Eu. The phosphor may be present as a ceramic layer, or may be present as particles in a host material, such as transparent ceramic, glass or silicone.

[0071] In an alternative embodiment, the specific second wavelength, i.e., the wavelength obtained from the conversion of the specific first wavelength, is about 610 nm to about 630 nm. A phosphor that can convert light to this wavelength is, for example, (Ca, Sr)AlSiN3:Eu 2+ 、(Sr,Ca)Al2Si2N6:Eu 2+ 、(Ba,Sr,Ca)2Si5N8:Eu 2+ 、Sr(LiA13N4):Eu 2+ The phosphor may be present as a ceramic layer, or may be present as particles in a host material, such as transparent ceramic, glass or silicone.

[0072] In an alternative embodiment, the specific second wavelength, i.e., the wavelength obtained from the conversion of the specific first wavelength, is greater than about 700 nm. The phosphor that can convert light to this wavelength is, for example, Cr 3+ / 4+ 、Ni 2+ , Bi, Yb, Tm, Er, etc. doped host crystals and glasses (e.g., La3Ga5GeO 14 、Ga2O3、Gd3Ga3Sc2O 12 , Mg2SiO4, etc.). The phosphor may be present as particles in a host material, such as transparent ceramic, glass or silicone.

[0073] The phosphor layer preferably has a similarly shaped structure. The thickness of the phosphor layer, ie the length that light traverses through the phosphor layer at a 90° angle relative to the emission source surface of the particular first wavelength of light, is for example 420nm to 465nm, preferably 445nm to 455nm.

[0074] In one embodiment, more than one phosphor layer is present, for example, 2, 3 or more layers are present.

[0075] The wavelength converter also includes a filter layer on top. The filter layer reflects unabsorbed excitation light of a specific first wavelength, for example, emitted from the LED die. The phosphor layer absorbs at least a portion of the light of the specific first wavelength and converts it to a specific second wavelength, and the filter layer reflects unabsorbed light of the specific first wavelength, while light of the specific second wavelength is transmitted.

[0076] The filter layer is directly attached to the phosphor layer. "Directly attached" in the context of the present invention means that there is at least one contact point between the phosphor layer and the filter layer. In a preferred embodiment, at least one surface of the phosphor layer is covered with a filter layer.

[0077] The filter layer of the invention may be a multilayer of alternative oxides. The filter may be made by vapor deposition or sputtering deposition of these oxide layers on a substrate. The substrate may be a phosphor layer, for example in the form of a ceramic. In this case, there is preferably no glue between the phosphor layer and the filter layer. Alternatively, the substrate may be a thin glass or sapphire layer. In this case, the coated glass (or sapphire) is the filter layer. The filter layer is preferably glued to the phosphor layer.

[0078] In one embodiment, the filter layer comprises at least two metal oxides. The metal oxides of the filter layer may be present in one layer. In an alternative aspect of this embodiment, the filter layer comprises several sub-layers. Each of the sub-layers may comprise at least one metal oxide.

[0079] The filter layer may be a dichroic filter. A dichroic filter, thin film filter, or interference filter is a very precise color filter used to selectively pass light of a small range of colors while reflecting other colors.

[0080] In a dichroic mirror or filter, alternating layers of optical coatings with different refractive indices are built onto a glass substrate. The interfaces between the layers of different refractive indices produce phase reflections that selectively enhance specific wavelengths of light and interfere with other wavelengths. The layers are typically added by vacuum deposition. By controlling the thickness and number of layers, the wavelength of the filter's passband can be adjusted and made wider or narrower as desired. Because the unwanted wavelengths are reflected rather than absorbed, the dichroic filter does not absorb this unwanted energy during operation and therefore does not get nearly as hot as an equivalent conventional filter (which attempts to absorb all energy except that in the passband).

[0081] The filter layer may comprise, for example, two sublayers each comprising a different metal oxide. Preferably, the metal oxides have contrasting refractive indices. In an alternative embodiment, the filter layer comprises three or more sublayers each comprising a different or identical metal oxide, wherein preferably, the sublayers of the same metal oxide are not attached to each other. Thus, the filter layer may comprise n sublayers and up to n different metal oxides. In a preferred embodiment, the filter comprises two metal oxides, one having a high refractive index and one having a low refractive index.

[0082] In one embodiment, the filter layer comprises 13 to 19 sublayers. In a preferred embodiment, the filter layer comprises 15 to 18 sublayers. In an even more preferred embodiment, the filter layer comprises 16 or 17 sublayers. In a further preferred embodiment, the filter layer comprises 17 sublayers.

[0083] The metal oxide of the filter layer can be selected from SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3. Preferred metal oxides are pairs of Al2O3-TiO2 or SiO2-Nb2O5.

[0084] 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 layers, L layers with different thicknesses, e.g., H, L, H, L, H, L, H, L, H, L, etc.

[0085] In one embodiment, the filter layer comprises 17 sub-layers and alternating sub-layers of two different metal oxides, such as Al2O3 and TiO2.

[0086] The filter layer preferably has a similarly shaped structure. The thickness of the filter layer, ie the length of the light traversing through the filter layer at 90° relative to the emission source surface of the light of the specific first wavelength, is for example 420nm to 465nm, preferably 445nm to 455nm.

[0087] The thickness of the sub-layers of the filter layer may each be from about 20 nm to about 150 nm. In one embodiment, the thickness of the sub-layers may each be from about 30 nm to about 40 nm.

[0088] The filter layer thickness is preferably related to the wavelength λ. The thickness is a multiple of half λ. In the present invention, a high reflectivity in the blue excitation light at wavelengths below the cut-off wavelength, for example below 535 nm, and a high transmittance in the amber phosphor emission region above the cut-off wavelength should be achieved.

[0089] The wavelength converter may also include an absorbing layer above the filter. The absorbing layer preferably absorbs light of wavelengths that will not pass through the filter layer to be emitted.

[0090] Examples of absorption layers are layers of ion-doped color filter glass comprising MoS2 dyed glass, Ce-doped gallium-gadolinium-YAG, or selected from semiconductor materials such as GaP, AlP, AlAs, CdSe, CdS in the form of thin layers or nanoparticles.

[0091] The absorbing layer is preferably attached to the filter layer.The absorbing layer may be attached to the filter layer with glue or may be attached due to inherent adsorption forces.

[0092] The filter layer preferably has a similarly shaped structure. The thickness of the filter layer, i.e. the length of the light traversing through the filter layer at a 90° angle relative to the emission source surface of the light of the specific first wavelength, is, for example, about 420nm to about 465nm, preferably about 445nm to 455nm.

[0093] The total thickness of the wavelength converter is about 20 μm to about 80 μm. In one embodiment, the thickness of the wavelength converter is about 40 μm to about 70 μm. In a preferred embodiment, the thickness of the wavelength converter is about 40 μm to about 50 μm. The thickness of the wavelength converter is the length of the wavelength converter that the light traverses through at a 90° angle relative to the emission source surface of the light of the specific first wavelength.

[0094] Another object of the present invention is to provide a light emitting device assembly, comprising:

[0095] LED die, and

[0096] A wavelength converter, the wavelength converter comprising:

[0097] a phosphor layer, and

[0098] Filter layer,

[0099] Wherein the filter layer is directly attached to the phosphor layer, and wherein the total thickness of the wavelength converter is from about 20 μm to about 80 μm.

[0100] The LED die preferably emits blue light. In an alternative embodiment, the LED die emits UV light. An example of an LED die is a GaN / InGaN based semiconductor material.

[0101] The wavelength converter, the phosphor layer and the filter layer correspond to the respective means as described above.

[0102] An object of the present invention is to provide a method for preparing a wavelength converter, the method comprising the following steps:

[0103] Provide glass substrate or sapphire wafer,

[0104] coating a glass substrate or a sapphire wafer with a filter layer comprising different metal oxides to prepare a coated glass substrate or a coated sapphire wafer,

[0105] providing a phosphor material, and

[0106] Attaching a coated glass substrate or a coated sapphire wafer to the phosphor material provides a wavelength converter,

[0107] Wherein the filter layer is directly attached to the phosphor layer, and wherein the total thickness of the wavelength converter is from about 20 μm to about 80 μm.

[0108] In a step of the method for producing 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 transmissive for the wavelength that should be emitted from the wavelength converter.

[0109] The thickness of the glass substrate or the sapphire wafer may be about 40 μm to about 200 μm. In one embodiment, the thickness of the glass substrate or the sapphire wafer may be about 40 μm to about 100 μm.

[0110] In another step, the glass substrate or sapphire wafer is coated with at least two layers of metal oxide to provide a coated glass substrate or a coated sapphire wafer. The coating is preferably carried out by depositing a pair of Al2O3-TiO2 oxides or SiO2-Nb2O5 oxides, however, other metal oxides may also be deposited on the glass substrate or sapphire wafer.

[0111] In one embodiment, coating is performed stepwise. Thus, a first layer of at least one metal oxide is coated on a glass substrate or a sapphire wafer. In a subsequent step, a second layer of at least one metal oxide is coated on the glass first layer of at least one metal oxide. Additional layers (if present) are introduced accordingly. As an optional step, there is a drying step between the coating steps or at least after the final coating step. Coating can be performed by vapor deposition or sputtering deposition.

[0112] In one embodiment of the present invention, the layer of metal oxide corresponds to a sublayer of the filter layer as mentioned herein, and the sum of all layers of metal oxide coated on the glass substrate or sapphire wafer corresponds to the filter layer as mentioned herein.

[0113] In one embodiment, the metal oxide is selected from SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3. Preferred metal oxides are paired Al2O3-TiO2 oxides or SiO2-Nb2O5 oxides.

[0114] In one embodiment, there are 17 layers of metal oxides coated on a glass substrate or sapphire wafer, and the metal oxides are Al2O3 and TiO2.

[0115] In another step, a phosphor material is provided. Exemplary phosphors are garnets, oxynitride silicates, perovskites, quantum dots, silicates, or combinations thereof, each doped with at least one suitable element.

[0116] In one embodiment, the phosphor material is selected from (Ba, Sr)2Si5N8:Eu 2+ 、Ca-α-SiAlON:Eu 2+ , YAG:Ce+CaA1SiN3:Eu, (Ca,Sr)AlSiN3:Eu 2+ 、(Sr,Ca)Al2Si2N6:Eu 2+ 、(Ba,Sr,Ca)2Si5N8:Eu 2+ and Sr(LiA13N4):Eu 2+ .

[0117] The phosphor (eg, the phosphor mentioned herein) may be selected from undoped (Ba, Sr) 2 Si 5 N 8 :Eu 2+ , Ca-α-SiAlON or AlN, or mixed with a glass host material composed of a low melting temperature glass, borosilicate glass or phosphate glass.

[0118] In a preferred embodiment, the phosphor layer is (Ba, Sr)2Si5N8:Eu 2+ , or (Ba,Sr)2Si5N8:Eu 2+ In a further preferred embodiment, the phosphor layer is (Ba, Sr) 2 Si 5 N 8 :Eu 2+ .

[0119] In an alternative embodiment, the phosphor layer comprises at least two different phosphors, at least three different phosphors, or at least four different phosphors.

[0120] In one embodiment, the specific second wavelength, i.e., the dominant wavelength obtained from the conversion of the specific first wavelength, is about 590 nm. A phosphor that can convert light to this wavelength is, for example, (Ba, Sr)2Si5N8:Eu 2+ 、Ca-α-SiAlON:Eu 2+ and YAG:Ce+CaA1SiN3:Eu. The phosphor may be present as a ceramic layer, or may be present as particles in a host material, such as transparent ceramic, glass or silicone.

[0121] In an alternative embodiment, the specific second wavelength, i.e., the wavelength obtained from the conversion of the specific first wavelength, is about 610 nm to about 630 nm. A phosphor that can convert light to this wavelength is, for example, (Ca, Sr)AlSiN3:Eu 2+ 、(Sr,Ca)Al2Si2N6:Eu 2+ 、(Ba,Sr,Ca)2Si5N8:Eu 2+ 、Sr(LiA13N4):Eu 2+ The phosphor may be present as a ceramic layer, or may be present as particles in a host material, such as transparent ceramic, glass or silicone.

[0122] In an alternative embodiment, the specific second wavelength, i.e., the wavelength obtained from the conversion of the specific first wavelength, is greater than about 700 nm. The phosphor that can convert light to this wavelength is, for example, Cr 3+ / 4+ 、Ni 2+ , Bi, Yb, Tm, Er, etc. doped host crystals and glasses (e.g., La3Ga5GeO 14 、Ga2O3、Gd3Ga3Sc2O 12 , Mg2SiO4, etc.). The phosphor may be present as particles in a host material, such as transparent ceramic, glass or silicone.

[0123] The coated glass substrate or coated sapphire wafer is attached to the phosphor material to provide a wavelength converter. In one embodiment, the attachment of the coated glass substrate or coated sapphire wafer to the phosphor material is performed by laminating the coated glass substrate or coated sapphire wafer to the phosphor material with glue.

[0124] The glue can be transparent epoxy, silicone, or polysiloxane.

[0125] In a preferred embodiment, the phosphor material is attached to the metal oxide layer and the glass substrate or sapphire wafer is opposite the phosphor material. In an alternative embodiment, the phosphor material is attached to a glass substrate, or sapphire wafer and the filter layer is opposite the phosphor layer.

[0126] In another embodiment, an absorbing layer as mentioned herein is attached to the filter layer.

[0127] In one embodiment, the wavelength converter is diced into smaller pieces. Typical sizes of the wavelength converter are 0.75 mm x 0.75 mm, 1 mm x 1 mm, or 2 mm. 2 In a preferred embodiment, the size of the wavelength converter is 1 mm x 1 mm.

[0128] Another object of the present invention is to provide a method for preparing a light emitting device assembly, comprising:

[0129] providing an LED die, optionally attached to a lead frame,

[0130] Attaching a wavelength converter to the LED die, the wavelength converter comprising:

[0131] a phosphor layer, and

[0132] Filter layer,

[0133] Wherein the filter layer is directly attached to the phosphor layer, and wherein the total thickness of the wavelength converter is from about 20 μm to about 80 μm.

[0134] The LED dies, phosphor layers, and filter layers correspond to respective devices as described herein.

[0135] In one embodiment, attachment of the wavelength converter is performed using silicone bonding to the LED die.

[0136] Another object of the present invention is to provide a wavelength converter prepared by the method of the present invention.

[0137] Another object of the present invention is to provide a light-emitting device prepared by the method of the present invention.

[0138] In one embodiment of the present invention, the wavelength converter of the present invention is used in LED packages for industrial and automotive lighting.

[0139] Figure 1 A typical microstructure of (Sr,Ba)2Si5N8:Eu amber ceramic is shown in Figure 1. The light-colored matrix phase is (Sr,Ba)2Si5N8. The darker phase is Ba1Si7N 10 There are also some holes in the ceramic. There can be a considerable amount of scattering in the amber ceramic. Since (Sr,Ba)2Si5N8 is not a cubic structure, the first scattering source comes from grain boundary scattering. The second scattering comes from Ba1Si7N 10 The third scattering comes from the holes due to the large refractive index contrast between the holes and the matrix.

[0140] Since there is usually significant scattering in amber ceramics, the total scattering depends on the thickness of the amber ceramic. The thicker the sample, the more scattering there is. Figure 2 Lumens of LEDs using amber ceramic disc converters with different thicknesses at 350 mA drive current are shown. Ld=447 nm means that the LED die emits blue light at a dominant wavelength of 447 nm. W / O casting means that there is no white silicone casting around the LED die and converter. Figure 2 It is clearly shown that as the thickness of the amber ceramic increases, the LED lumens decrease. This is due to more scattering which reduces the packaging efficiency.

[0141] It would seem natural that thinner amber ceramics would be preferred due to their higher package lumens. Figure 3 The color of amber ceramic LEDs with various thicknesses is shown in the figure, with the color of the thinnest amber ceramic LED falling outside the required color specification. The larger dashed box is the ECE (Economic Commission for Europe) amber color requirement. Although thinner amber ceramics obtain higher package lumens, they cannot absorb all blue light and therefore have more residual blue light. More residual blue light leads to a reduction in color Cx. As the thickness increases, the emission color gradually shifts to a higher emission dominant wavelength. This is due to self-absorption of thick samples.

[0142] The current standard thickness of amber ceramics in wavelength converters is about 120 μm. Such a thickness will ensure that the ceramic is thick enough to absorb most of the light of a specific first wavelength, such as blue light. The sheet thickness is reduced to about 90 μm and about 70 μm. The color and conversion efficiency CE are measured by an internal pinhole device OSRAM tester. A stable and constant blue light passes through the pinhole on which the sheet sample is placed. The residual blue light transmitted forward and the emitted amber light are collected by a small integrating sphere above the sample. The color and conversion efficiency CE (forward lumens divided by the incident blue power, lm / W_b) are measured.

[0143] Figure 4 The color distribution of amber ceramic sheets with 120 μm, 90 μm and 70 μm is shown. For the standard thickness of 120 μm, the average CE of the sheets is 91.4 Im / W. As the thickness decreases to 90 μm and 70 μm, the CE increases to 96.4 Im / W to 98 Im / W, respectively.

[0144] A wavelength converter with filter layers according to the invention was prepared. The phosphor material was a layer of amber ceramic. The filter consisted of 17 sub-layers of alternating materials Al2O3 and TiO2 with low and high refractive index.

[0145] (Table 1: Filter design)

[0146] Sublayer number Filter layer Thickness [nm] 1 <![CDATA[Al2O3]]> 37 2 <![CDATA[TiO2]]> 43 3 <![CDATA[Al2O3]]> 63 4 <![CDATA[TiO2]]> 50 5 <![CDATA[Al2O3]]> 62 6 <![CDATA[TiO2]]> 51 7 <![CDATA[Al2O3]]> 66 8 <![CDATA[TiO2]]> 50 9 <![CDATA[Al2O3]]> 68 10 <![CDATA[TiO2]]> 49 11 <![CDATA[Al2O3]]> 65 12 <![CDATA[TiO2]]> 51 13 <![CDATA[Al2O3]]> 68 14 <![CDATA[TiO2]]> 48 15 <![CDATA[Al2O3]]> 54 16 <![CDATA[TiO2]]> 53 17 <![CDATA[Al2O3]]> 127 Air

[0147] Table 1

[0148] Figure 5 The simulated reflectivity curve according to the filter design in Table 1 is shown in FIG. It shows a high reflectivity from 410 nm to 500 nm. The reflectivity drops rapidly above 500 nm, with a cut-off wavelength at about 530 nm. Such a coating can be made on an amber ceramic sheet by electron beam evaporation, sputtering or other coating methods. The amber sheet before and after coating is measured by an OSRAM tester. The measurement results are compared with Figure 5 The simulated reflectivity curves of the midcoat are compared. After coating, the residual blue light around 450nm is greatly reduced, while the amber emission around 600nm is slightly increased.

[0149] Figure 6 The color distribution of amber ceramic sheets with 120 μm, 90 μm and 70 μm before and after coating was compared. The Cx of all coated sheets increased. The thinner the coated sheet, the more its Cx increased. The CE of the coated sheet was about 1% higher than before the sheet was coated.

[0150] The coated flakes were assembled in an LED package along with an uncoated manufactured amber flake as a reference. The emission color of the coated amber flake in the package ( Figure 7 )and Figure 6 The color measured by the Osram tester is very similar. The package lumens @ 700mA of the coated amber tablets are 5% to 18% higher than the reference uncoated tablets ( Figure 8 ).

[0151] In some embodiments, amber ceramic surface finishing is another aspect of the coating process. Fig. 9 An SEM image of a cross section of a coated amber ceramic is shown. The ceramic surface, like the ground, is not perfectly flat. Surface imperfections can negatively impact the coating in two ways. First, they can reduce the quality of the coating. Second, they can introduce scattering into the coating that will affect the angle of incidence of the light. The reflectivity of the coating can depend on the angle of incidence of the light. As the angle of incidence increases, Figure 5 The reflectivity curve in will shift to the left and the cut-off wavelength will decrease. Scattering caused by defects in the surface can therefore change the reflectivity / transmittance. For coating purposes, a polished surface with an amber ceramic is preferred.

[0152] Amber sheets with a thickness of 70 μm, 90 μm and 120 μm were polished down to 1 μm with diamond slurry. The polished sheets and the ground sheets were then coated with a layer according to Table 2.

[0153] Sublayer number Filter layer Thickness [nm] 1 <![CDATA[Al2O3]]> 32.7 2 <![CDATA[TiO2]]> 53.1 3 <![CDATA[Al2O3]]> 55 4 <![CDATA[TiO2]]> 51.3 5 <![CDATA[Al2O3]]> 67 6 <![CDATA[TiO2]]> 53.9 7 <![CDATA[Al2O3]]> 60.9 8 <![CDATA[TiO2]]> 56 9 <![CDATA[Al2O3]]> 68.1 10 <![CDATA[TiO2]]> 46.4 11 <![CDATA[Al2O3]]> 71.1 12 <![CDATA[TiO2]]> 59.6 13 <![CDATA[Al2O3]]> 48.9 14 <![CDATA[TiO2]]> 52.4 15 <![CDATA[Al2O3]]> 63 16 <![CDATA[TiO2]]> 57.1 17 <![CDATA[Al2O3]]> 128.8 Air

[0154] Table 2

[0155] The coated polished and unpolished wafers were measured by OSRAM tester ( Fig.10 ). All polished flakes were more saturated in color than the unpolished flakes, as indicated by the increase in Cx, meaning that less residual blue was present in the coated polished flakes. Their CE was also 1% to 2% higher.

[0156] Another embodiment is a stack of a thin assembly of phosphor layers and filter layers with another transparent layer ( Fig.11 ), the transparent layer is preferably glass, Al2O3, or silicone. Between the transparent layer 5 and the phosphor layer 2 is the filter layer 3. The filter layer can be first applied to the transparent layer 5 in a high volume process and then glued to the phosphor layer 2 by a transparent epoxy resin, silicone, or polysiloxane, water glass or low melting glass (e.g., (Sr,Ba)2Si5N8 amber ceramic).

[0157] The advantage of this embodiment is that a transparent layer such as glass can have a much smoother surface than ceramic. Therefore, the filter layer on such a phosphor layer can have a better quality. Since the present disclosure uses a thinned amber ceramic with less scattering, a possible problem is that the height of the ceramic is lower than the highest point of the bond line ( Fig.12 ). The highest part of the wire cannot be covered by a casting protection material such as silicone. Therefore, another advantage of this embodiment is that the total thickness of the hybrid circuit can be adjusted so that it is higher than the bonding wire, so that the entire bonding wire can be protected by the sidewall protection casting in the package ( Fig.12 ).

[0158] Fig.13 An exemplary method for preparing a wavelength converter is shown. In a first step, the filter layer 3 is deposited on a glass substrate or a sapphire wafer 8. The phosphor layer 2 is attached to the filter layer with glue 9. This produces a so-called multilayer stack. In another step, the multilayer stack is diced into smaller pieces in a subsequent step.

[0159] Fig.14 One exemplary method for preparing a light emitting device assembly 6 is shown. In a first step, a wavelength converter 1 is attached to an LED die 7, which is attached to a lead frame 10. Bonding wires 11 are attached to the LED die 7. In a subsequent step, the assembly is molded with a molding tool 12 in a transfer molding step, and there is a protective silicone casting 13. After the molding step, a light emitting device assembly 6 is obtained.

[0160] Fig.15 An exemplary thick ceramic is shown, while Fig.16 The thin ceramic of the invention is shown, in which the conversion of blue light to longer wavelength light in the converter ceramic generates heat due to Stokes shift losses. This leads to a temperature increase in the ceramic element. The thermal resistance of the converter element increases with thickness, and thus the maximum temperature increases with thickness. The conversion efficiency decreases with temperature, and the degradation increases. Reducing the thickness of the ceramic thus improves the performance of the conversion LED, especially in LEDs with current densities > 1 A / mm 2 performance in high power applications. Therefore, thin ceramic layers with coating d < 70 μm are better than thick layers. In conclusion, R th _ 厚 >R th _ 薄 Lead to T 厚 >T 薄 .

[0161] Fig.17The reflective properties of the coating are shown. One problem is that the reflection band of the dielectric coating is shifted in wavelength with the angle of incidence. 100% reflection of a wide blue LED (FWHM about 25 nm) cannot be ensured for all angles of incidence. So, for example, the color is less saturated for high angles of incidence. One possible solution is to add a wavelength selective absorption layer on top of the filter layer, which causes absorption of blue light and therefore transmission of light of longer wavelengths. Most of the unabsorbed blue light (e.g. >90%) is reflected by the filter layer and the remaining part is absorbed by the blue filter. The filter layer band and the blue LED should be adjusted so that normal incidence is best reflected and higher angles are partially transmitted because the optical path length in the absorption layer is longer for higher angles of incidence.

[0162] Fig.18 The color of an LED with a ceramic layer as seen from different viewing angles is shown. 0° is viewing along the optical axis, higher angles are oblique viewing. While the color shift between straight-on and oblique viewing is low for a thick ceramic layer without a mirror (2), the color can change significantly for the case of a thin ceramic layer with a dielectric filter (1). This case may require blocking of light from oblique angles, additional mixing optics, or additional absorbing layers on top of the mirror as described.

[0163] Fig.19 Different embodiments of the wavelength converter 1 are shown. The absorption layer 4 can be deposited directly on top of the filter layer 3, or on the underside or on the upper side of a glass substrate or sapphire wafer 8. Another option is to coat the blue filter glass with the filter layer 3. Materials for the absorption layer may include: ion-doped glass (Schott filter glass), converter materials with high activator concentration and high quenching, or thin coating semiconductor materials specifically for having a band gap larger than the emission (e.g. GaP or similar for yellow).

[0164] Using the methods and apparatus described herein, thinner ceramics have the advantage of higher efficiency while ensuring that their color falls within color requirements.

[0165] Typically, thick layers of wavelength converters are generally inefficient due to scattering, however they generally have high color saturation. Typically, the thinner the wavelength converter, the less scattering occurs in combination with higher efficiency, but low color saturation. The wavelength converters of the present invention exhibit low scattering, low back reflection, high efficiency and good saturation.

[0166] While there have been shown and described what are presently considered to be preferred embodiments of the present invention, it will be apparent to those skilled in the art that various changes and modifications may be made herein without departing from the scope of the invention as defined by the appended claims. The present disclosure also includes any novel features and any combination of features, which in particular includes any combination of features in the appended claims, even if the feature or combination itself is not explicitly pointed out in the claims or examples.

[0167] This patent application claims priority to U.S. patent application 16 / 269,442, the contents of which are incorporated herein by reference.

Claims

1. A wavelength converter, comprising: a phosphor layer; and Filter layer, wherein the filter layer comprises a coated glass substrate or a coated sapphire wafer, and wherein the filter layer is directly attached to the phosphor layer, wherein the total thickness of the wavelength converter is 20 μm to 80 μm, and wherein the filter layer comprises at least two different metal oxides selected from SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3, wherein the at least two different metal oxides are characterized by contrasting refractive indices, and The at least two different metal oxides are arranged such that layers with a high refractive index alternate with layers with a low refractive index.

2. The wavelength converter according to claim 1, wherein the phosphor of the phosphor layer is selected from (Ba, Sr)2Si5N8:Eu 2+ 、Ca-α-SiAlON:Eu 2+ , YAG:Ce+CaA1SiN3:Eu, (Ca,Sr)AlSiN3:Eu 2+ 、(Sr,Ca)Al2Si2N6:Eu 2+ 、(Ba,Sr,Ca)2Si5N8:Eu 2+ and Sr(LiA13N4):Eu 2+ . The wavelength converter according to claim 1 , further comprising an absorption layer.

4. The wavelength converter according to claim 3, wherein the absorption layer is selected from ion-doped color filter glass, or selected from semiconductor materials, the ion-doped color filter glass comprising MoS2 dyed glass, Ce-doped gallium-gadolinium-YAG. 5 . The wavelength converter according to claim 4 , wherein the semiconductor material comprises GaP, AlP, AlAs, CdSe or CdS in the form of a thin layer or in the form of nanoparticles.

6. A light emitting device assembly, comprising: LED die; and A wavelength converter, the wavelength converter comprising: a phosphor layer; and Filter layer, wherein the filter layer comprises a coated glass substrate or a coated sapphire wafer, and wherein the filter layer is directly attached to the phosphor layer, wherein the total thickness of the wavelength converter is 20 μm to 80 μm, and wherein the filter layer comprises at least two different metal oxides selected from SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3, wherein the at least two different metal oxides are characterized by contrasting refractive indices, and The at least two different metal oxides are arranged such that layers with a high refractive index alternate with layers with a low refractive index.

7. A method for preparing a wavelength converter, the method comprising: Provide glass substrate or sapphire wafer, coating the glass substrate or the sapphire wafer with a filter layer comprising at least two different metal oxides to prepare a coated glass substrate or a coated sapphire wafer, providing a phosphor material, and attaching the coated glass substrate or the coated sapphire wafer to the phosphor material, thereby providing a wavelength converter including a phosphor layer, wherein the filter layer is directly attached to the phosphor layer, wherein the total thickness of the wavelength converter is 20 μm to 80 μm, and wherein the at least two different metal oxides are selected from SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3, wherein the at least two different metal oxides are characterized by contrasting refractive indices, and The at least two different metal oxides are arranged such that layers with a high refractive index alternate with layers with a low refractive index.

8. The method according to claim 7, wherein the phosphor material is selected from (Ba, Sr)2Si5N8:Eu 2+ 、Ca-α-SiAlON:Eu 2+ , YAG:Ce+CaA1SiN3:Eu, (Ca,Sr)AlSiN3:Eu 2+ 、(Sr,Ca)Al2Si2N6:Eu 2+ 、(Ba,Sr,Ca)2Si5N8:Eu 2+ and Sr(LiA13N4):Eu 2 .

9. The method of claim 7, wherein attaching 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 glue.

10. The method of claim 7, further attaching an absorbing layer to the wavelength converter. The method of claim 7 , further comprising scribing the wavelength converter.

12. A wavelength converter prepared according to the method of claim 7.

13. A method for preparing a light emitting device assembly, comprising: Provide LED die; as well as attaching a wavelength converter to the LED die, the wavelength converter comprising a phosphor layer and a filter layer comprising at least two different metal oxides, wherein the filter layer comprises a coated glass substrate or a coated sapphire wafer, and wherein the filter layer is directly attached to the phosphor layer, wherein the total thickness of the wavelength converter is 20 μm to 80 μm, and wherein the at least two different metal oxides are selected from SiO2, Al2O3, TiO2, Nb2O5, Ta2O5, HfO2 and Y2O3, wherein the at least two different metal oxides are characterized by contrasting refractive indices, and The at least two different metal oxides are arranged such that layers with a high refractive index alternate with layers with a low refractive index.

14. The method of claim 13, wherein the LED die is selected from GaN / InGaN based semiconductor materials.

15. A light emitting device assembly prepared according to the method of claim 13.

Images