HK1162082B - A light emitting device having a refractory phosphor layer - Google Patents

Description

Light emitting device with refractory phosphor layer

Technical Field

The present invention relates to a light emitting device, and more particularly, to a semiconductor light emitting device having a refractory phosphor layer.

Background

Light Emitting Diodes (LEDs) are attractive alternatives for replacing conventional Light sources, such as incandescent and fluorescent Light sources. LEDs have a substantially higher light conversion efficiency than incandescent lamps and have a longer lifetime than both types of conventional light sources. In addition, certain types of LEDs currently have higher conversion efficiencies than fluorescent light sources, and higher conversion efficiencies are demonstrated in the laboratory. Furthermore, LEDs require lower voltages than fluorescent lamps, and are therefore more suitable for applications where the light source must be powered from a low voltage source (e.g., a battery or an internal computer DC power supply).

Unfortunately, LEDs produce light in a relatively narrow spectral band. To replace conventional light sources, LEDs are required that produce light that appears "white" to the viewer. A light source appearing white with a conversion efficiency comparable to that of a fluorescent light source can be constructed from a blue light emitting diode covered with a fluorescent layer converting a portion of the blue light into yellow light. If the ratio of blue to yellow light is chosen correctly, the resulting light source appears white to the viewer. However, in applications requiring higher illumination power, the phosphor layer may overheat. If the heat is not dissipated sufficiently, this can lead to premature degradation of the phosphor layer and reduce device performance and lifetime.

To prevent the phosphor layer from overheating, many existing devices are designed such that the phosphor layer is further away from the light emitting semiconductor. However, this method creates additional problems. As the distance between the phosphor layer and the light emitting semiconductor increases, the size of the device increases, thereby increasing the manufacturing cost of the device. Furthermore, this design does not effectively address the heat dissipation problem, as it does not provide any means for dissipating heat from the phosphor layer.

Thus, while existing LEDs have proven generally suitable for their intended use, they have inherent drawbacks that reduce their overall effectiveness and desirability. As such, there is a need for small, high power "white" LEDs with a system for dissipating heat from the phosphor layer.

Disclosure of Invention

In one aspect of the present disclosure, a light emitting device includes a transparent thermally conductive layer, a refractory phosphor layer provided on the transparent thermally conductive layer, and a light emitting semiconductor configured to emit light toward the transparent thermally conductive layer and the refractory phosphor layer.

In another aspect of the present disclosure, a light emitting device includes a refractory phosphor layer fused on a transparent layer having a higher thermal conductivity than that of the refractory phosphor layer.

In another aspect of the present disclosure, a method for manufacturing a light emitting device includes depositing at least one phosphor mixture on a transparent substrate, wherein the phosphor mixture includes a phosphor, a glass frit, and a binder.

In another aspect of the present disclosure, a method for manufacturing a light emitting device includes fusing a refractory phosphor layer on a transparent layer.

It is understood that other aspects of the light emitting device will become readily apparent to those skilled in the art from the following detailed description, which is shown and described by way of illustration only, in the examples of various aspects of the light emitting device. As will be realized, the various aspects of the light emitting devices disclosed herein can be modified in various other respects, all without departing from the spirit and scope of the present invention. The drawings and detailed description are, therefore, to be regarded as illustrative in nature and not as restrictive.

Drawings

The various aspects of the disclosure are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which:

fig. 1 is a sectional view illustrating an example of a light emitting device;

fig. 2 is a sectional view illustrating an example of a light emitting device having a refractory phosphor layer; and is

Fig. 3 is a flowchart illustrating an example of a process for providing a refractory phosphor layer on a transparent layer.

Detailed Description

The detailed description set forth below in connection with the appended drawings is intended as a description of various aspects of light emitting devices and is not intended to represent all the ways in which the various aspects of the present invention may be practiced. The detailed description may include specific details for the purpose of providing a thorough understanding of various aspects of the light emitting device; it will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In some instances, well-known structures and components are schematically depicted and/or shown in block diagram form in order to avoid obscuring the concepts of the present invention.

Furthermore, the various descriptive terms used herein (e.g., "provided at …" and "transparent") should be given the broadest possible meaning within the context of the present disclosure. For example, when the phrase "providing a layer over another layer" is used, it is to be understood that one layer may be deposited, etched, attached, or otherwise prepared or fabricated directly or indirectly over the other layer. Moreover, describing something as "transparent" should be understood as having properties that do not allow electromagnetic radiation to be significantly blocked or absorbed at the particular wavelength (or wavelengths) of interest.

Fig. 1 is a sectional view illustrating an example of a light emitting device 100. In this example, the device may include a blue light emitting semiconductor 102 provided within a concave shell 104. The light emitting semiconductors 102 may be driven by a power source (not shown) that is electrically coupled to the light emitting semiconductors 102 by conductive traces (not shown). The concave shell 104 may be formed by drilling a cavity 106 (e.g., a conical cavity) in a layer of material (e.g., ceramic, resin, polyphthalate, polycarbonate, or other suitable material). The inner wall 108 of the concave shell 104 is coated with a reflective material (e.g., aluminum, silver, or a suitable plastic that is poured by injection molding with titanium dioxide). The cavity 106 may be filled with a rate matching material (e.g., silicone), or reduced oxygen (e.g., nitrogen). Thereafter, a fluorescent layer 110 covering the cavity 106 may be provided on the concave shell 104.

The fluorescent layer 110 is used in combination with the light emitting semiconductor 102 to generate light having a color temperature range and a spectral composition. The fluorescent layer 110 may include a mixture of silicone and fluorescent particles uniformly distributed and suspended in the silicone. The phosphor particles may be of different colors (e.g., yellow, red, blue) to enhance the color rendering index of the light generated by the device 100. The fluorescent layer 110 may have a disc shape to provide a uniform radiation pattern.

During operation, the light emitting semiconductor 102 may emit blue light. A portion of the blue light may be absorbed by the phosphor particles of the phosphor layer 110 and the remaining blue light may pass through the phosphor layer 110. Once blue light is absorbed by the phosphor particles, the phosphor particles may emit light of their respective colors. This secondary emission of colored light (also called stokes shift) from the fluorescent particles is optically mixed with the remaining blue light, so that the resulting mixed spectrum is perceived as white by the human eye.

Unfortunately, the Stokes shift used in phosphors to convert blue light to other wavelengths is not 100% efficient. The individual blue light photons absorbed by the phosphor particles do not always produce photons of different wavelengths. This lost energy is absorbed by the phosphor and dissipated as heat into the phosphor layer 110. For smaller devices, this heat generated is minimal and generally has no significant effect on the performance of the device. But for more powerful devices (e.g., those that consume more than 1 watt of power), the heat generated within the phosphor layer can become significant if not adequately dissipated. Excessive heat can degrade the phosphor layer and reduce its efficiency. That is, the phosphor layer will still absorb the same amount of optical radiation power, but will emit less light. As a result, the luminance may decrease and the color temperature may shift from white to blue, adversely affecting the performance of the device 100. In order to dissipate heat generated inside the fluorescent layer 110, a heat dissipation structure may be integrated into the light emitting device, as shown in fig. 2.

Fig. 2 is a cross-sectional view illustrating an example of a device 200 having a heat dissipation structure using a refractory phosphor layer 214. The light emitting semiconductor 202, the concave shell 204, the reflective inner wall 208, and the cavity 206 of fig. 2 correspond to the light emitting semiconductor 102, the concave shell 104, the reflective inner wall 108, and the cavity 106 of fig. 1, respectively, and as such, their respective descriptions are omitted. The heat dissipation structure of the device 200 may include a transparent layer 210, a metal shell 216, a metal substrate 218, and fins 220. The metal shell 216, metal substrate 218, and fins 220 may all be comprised of a thermally conductive material, such as copper, aluminum nitride, or diamond.

The fluorescent layer 214 may be fused to the transparent layer 210 to form an integrated glass-like layer. The transparent layer 210 may be a transparent and thermally conductive material, such as glass, sapphire, or diamond. After being fused on the transparent layer 210, the fluorescent layer 214 may be a refractory glass-like layer including fluorescent particles of one color or multiple colors (e.g., yellow, red, green). The process of fusing the fluorescent layer 214 on the transparent layer 210 will be described later in detail with reference to fig. 3.

Once fused, a phosphor layer 214 and a transparent layer 210 may be provided over the concave shell 204 and covering the cavity 206. Although fig. 2 shows the fluorescent layer 214 overlying the transparent layer 210, the order of the layers may be reversed such that the fluorescent layer 214 underlies the transparent layer 210.

Optionally, a mirror 212 (e.g., a Bragg mirror (DBR)) may be provided below the transparent layer 210 and the fluorescent layer 214. For example, the mirror 212 may include alternating layers of titanium dioxide and silicon dioxide of a particular thickness. The reflector 212 may be designed to transmit short wavelength light (e.g., blue) emitted through the light emitting semiconductor 202, but reflect longer wavelength light (e.g., red, yellow) emitted through the fluorescent layer 214. This prevents light emitted by phosphor layer 214 from entering cavity 206 (where light emitted by phosphor layer 214 becomes lost), but instead reflects such light out of device 200. Likewise, the mirror 212 may improve the efficiency of the device 200.

The concave shell 204 may be provided inside a metal housing composed of a metal shell 216 and a metal substrate 218, and the concave shell 204 includes the light emitting semiconductor 202, the fluorescent layer 214, the transparent layer 210, and the reflective mirror 212. The metal shell 216 may be bonded to the metal substrate 218 by capacitive discharge welding or other suitable methods. The concave shell 204 may be bonded to the metal substrate 218 by a suitable chemical bonding method and/or a mechanical bonding method. Once inside the metal housing, the phosphor layer 214, the transparent layer 210, and the mirror 212 may be protected from the concave shell 204 by a method suitable for sealing the cavity 206. For example, by mechanically folding the edges of the metal shell 216, the layers 214, 210, 212 may curl about the concave shell 204, as shown in FIG. 2. By hermetically sealing the device 200 in this manner, the device 200 is configured to withstand extreme fluctuations in temperature, pressure, and other environmental conditions.

In addition to providing a hermetic seal, the fluorescent layer 214 and the transparent layer 210 are thermally coupled to the metal shell 216 by the metal shell 216 curling layers 214, 210, 212, the metal shell 216 itself being thermally coupled to the metal substrate 218 and the fins 220, forming a thermally conductive path for the heat dissipating structure.

During operation of the device 200, heat generated by the phosphor particles in the phosphor layer 214 may be dissipated from the phosphor layer 214 to the metal shell 216 through the phosphor layer 214 itself and the transparent layer 210. The metal shell 216 transfers heat to the metal substrate 218, which in turn, dissipates the heat to the external environment through the fins 220 by the metal substrate 218. Also, the phosphor layer 214 is cooled, preventing the degradation of the phosphor layer 214.

Fig. 3 is a flow chart illustrating an example 300 of a process for combining the fluorescent layer 214 and the transparent layer 210. Processing begins and proceeds to block 302, where the various components of the fluorescent layer 214 are mixed. For example, a specific amount of phosphor may be mixed with a specific amount of glass frit, organic binder, and vitreous flux. For example, the phosphor may be a specific color or a combination of various colors (e.g., yellow, red, green), and a specific type, for example, a garnet-structure phosphor (e.g., yttrium aluminum garnet, terbium aluminum garnet), a sulfide phosphor (e.g., zinc sulfide, strontium sulfide), a selenide phosphor (cadmium selenide, zinc selenide), a silicate phosphor (e.g., barium silicate, strontium silicate, calcium silicate), and an alkali halide phosphor (e.g., cesium chloride, potassium bromide). The phosphor may include phosphor particles having a diameter of about 3 to 25 μm, but is not limited thereto. The glass frit may be any suitable type of glass frit. The organic binder may be any suitable organic diffuser that evaporates when heated to 600 degrees celsius or below 600 degrees celsius and may include compounds such as zinc oxide, lead oxide, and borax. The phosphor, glass frit, organic binder, and vitreous flux may be mixed to effectively mix and degas the mixture such that the phosphor particles are suspended and uniformly distributed within the mixture and the mixture is completely free of bubbles.

Once the mixture is ready, the process proceeds to block 304 where the mixture is uniformly deposited on a transparent substrate (e.g., transparent substrate 210) by screen printing, stencil printing, or other suitable method. For this purpose, for example, light-emitting devices for producing circuit boards can be used. For example, the mixture may be deposited to cover all or part of the transparent layer, as a continuous layer, a particular pattern, or an array of dots. The thickness of the deposited mixture can be controlled to obtain the desired final thickness of the phosphor layer.

After depositing the mixture, the process proceeds to block 306, where a determination is made as to whether all of the desired phosphors are present on the transparent layer. If it is determined that not all of the desired phosphor is present on the transparent layer, the process passes to block 308. At block 308, the mixture is dried for a predetermined amount of time and processing proceeds back to block 302 where another type and/or color of phosphor is mixed with the glass frit, organic binder, and glass-like flux. The process then proceeds down through blocks 302 to 306 until all of the desired phosphor is present on the transparent layer.

Where the process undergoes iterations in block 304 for each different phosphor, each phosphor mixture may be deposited as a particular pattern and/or array of dots on the transparent layer. Thus, the resulting phosphor layer may be a combination of patterns and/or dot arrays of different phosphor blends. The phosphor layer can be realized with a specific lithographic pattern when screen printing the respective mixture. The array may be such that each phosphor mixture is deposited so long as it does not overlap with an adjacent phosphor mixture. It is desirable to deposit different color phosphors in such an array to reduce the absorption of light by adjacent phosphor particles of different colors. In addition, separately depositing each phosphor mixture takes into account the presence of incompatible phosphor mixtures in the resulting phosphor layer, where the incompatible phosphor mixtures are located in each region within its array.

If it is determined at block 306 that all of the desired phosphors are present on the transparent layer, the process proceeds to block 310.

At block 310, the transparent layer with the deposited mixture is heated in a furnace, wherein the mixture is fused to the transparent layer. For example, the furnace may be a multi-zone belt furnace in which the mixture is heated to a particular temperature (e.g., 600 degrees celsius), cooled, and annealed for a period of 30 to 40 minutes. As the mixture melts and fuses to the transparent layer, it acquires refractive glass-like properties (i.e., becomes a refractive fluorescent layer). Due to the similar inorganic composition of the refractive fluorescent and transparent layers, the resulting bond between these layers may comprise superior chemical and optical properties.

After the refractive fluorescent layer is fused to the transparent layer in block 310, processing proceeds to block 312 where the refractive fluorescent layer and transparent layer are cut into pieces of a predetermined shape (e.g., circular, square) by a die cutter or similar light emitting device. Following block 312, processing is complete.

Each sheet is tested for various performance characteristics (e.g., color temperature) before being attached to its respective optical device (e.g., device 200 shown in fig. 2).

LEDs having heat dissipation structures that include a refractive phosphor layer may be used in many applications. By way of example, these LEDs are well suited for Liquid Crystal Display (LCD) backlighting applications. Other applications may include, but are not limited to, automotive interior lighting, light bulbs, lanterns, street lights, flashlights, or any other application where LEDs may be used.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more. The term "some" means one or more unless specifically stated otherwise. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Furthermore, no disclosure herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under 35u.s.c. § 112, sixth section unless the element is explicitly recited using the phrase "means for" or, in the case of a method claim, the element is explicitly recited using the phrase "step for".

Claims (15)

1. A light emitting device, comprising:

a transparent thermally conductive layer, wherein the transparent thermally conductive layer is coupled to a thermally conductive housing, the thermally conductive housing comprising a concave shell having a cavity and a metal shell, wherein the concave shell having a cavity is disposed inside the metal shell, the cavity being sealed;

a reflecting layer is arranged on the inner wall of the cavity;

a refractory phosphor layer disposed on the transparent heat conductive layer, wherein the refractory phosphor layer is fused to the transparent heat conductive layer, and the cavity is sealed by the transparent heat conductive layer provided with the refractory phosphor layer, and the transparent heat conductive layer provided with the refractory phosphor layer is crimped between the concave shell and a portion of the metal housing; and

a light emitting semiconductor configured to emit light toward the transparent thermally conductive layer and the refractory phosphor layer, wherein light not emitted toward the refractory phosphor layer is reflected by the reflective layer.

2. The light emitting device of claim 1, wherein the transparent thermally conductive layer is configured to dissipate heat from the refractory phosphor layer.

3. The light emitting device of claim 1, further comprising a bragg mirror disposed below the refractory phosphor layer.

4. The light emitting device of claim 1, wherein the metal housing is configured to dissipate heat from the refractory phosphor layer.

5. The light emitting device of claim 1, wherein the refractory phosphor layer comprises a plurality of phosphor components.

6. The light emitting apparatus of claim 5 wherein the phosphor component is an array of phosphor dots.

7. The lighting device of claim 5, wherein said phosphor component is a plurality of individual phosphor patterns.

8. The lighting apparatus of claim 5, wherein at least one of said phosphor sections is configured to produce light of a different color than light produced by at least another one of said phosphor sections.

9. The light emitting device of claim 5, wherein at least one of the phosphor sections includes phosphor particles of a different type than phosphor particles included in at least another one of the phosphor sections.

10. The light emitting device of claim 1, wherein the transparent thermally conductive layer is formed from a material selected from the group consisting of glass, sapphire, and diamond.

11. A light emitting device, comprising:

fusing the refractory phosphor layer onto a transparent heat conducting layer comprising a higher thermal conductivity than a thermal conductivity of the refractory phosphor layer, wherein the transparent heat conducting layer is coupled to a heat conducting housing comprising a recessed shell having a cavity and a metal casing, wherein the recessed shell having a cavity is disposed inside the metal casing, the cavity is sealed by the transparent heat conducting layer provided with the refractory phosphor layer, and the transparent heat conducting layer provided with the refractory phosphor layer is crimped between the recessed shell and a portion of the metal casing; and

a reflective layer is disposed on the inner wall of the cavity, wherein the reflective layer is configured to reflect light toward the transparent thermally conductive layer.

12. A method of manufacturing a light emitting device, the method comprising:

depositing at least one phosphor mixture on the transparent thermally conductive layer, wherein the phosphor mixture comprises phosphor, glass frit, and a binder;

fusing the phosphor mixture to the transparent thermally conductive layer;

thermally coupling said transparent thermally conductive layer to a thermally conductive housing comprising a concave shell having a cavity and a metal shell, wherein said concave shell having a cavity is disposed inside said metal shell, said cavity is sealed by said transparent thermally conductive layer with said phosphor mixture, and said transparent thermally conductive layer with said phosphor mixture is crimped between said concave shell and a portion of said metal shell; and

depositing a reflective layer on the inner wall of the cavity, wherein the reflective layer is configured to reflect light toward the transparent thermally conductive layer.

13. The method of claim 12, further comprising more than one of the phosphor mixtures, wherein one of the phosphor mixtures is deposited in a first array of phosphor sections and another of the phosphor mixtures is deposited in a second array of phosphor sections such that the phosphor sections of the first array do not overlap the phosphor sections of the second array.

14. The method of claim 13, wherein at least one of the phosphor blends is configured to produce light of a different color than light emitted by at least another one of the phosphor blends.

15. The method of claim 13, wherein at least one of the phosphor blends includes different types of phosphor particles than at least one other of the phosphor blends.