Patent Application
20150276172
1. Field
The present disclosure relates generally to a light-emitting device and, more particularly, to a light-emitting device with a reflective ceramic substrate.
2. Background
A light-emitting device may include a substrate located between light-emitting diodes and a heat sink. Different substrates may have different thermal conductivities, different electrical conductivities, and/or different conversion efficiencies. A substrate with low thermal conductivity may transfer relatively less heat from the light-emitting diodes to the heat sink, thereby causing the light-emitting diodes to overheat. A substrate with high electrical conductivity may allow relatively more power to escape through the substrate, thereby decreasing power efficiency of the light-emitting device. A substrate with low conversion efficiency may have relatively high light-absorption, thereby decreasing the total emission of light from the light-emitting device.
In existing systems, the substrate may include sapphire or silicon. However, sapphire has low thermal conductivity, and silicon has high electrical conductivity and low conversion efficiency. Although an electrical insulator may be added between a silicon substrate and the heat sink in order to reduce electrical conductivity, providing such an additional layer adds manufacturing steps and production costs. Therefore, a need exists for a substrate that has high thermal conductivity, dielectric properties, and high conversion efficiency, without requiring additional manufacturing steps.
Several aspects of the present invention will be described more fully hereinafter with reference to various apparatuses.
One aspect of a light-emitting device is disclosed. A light-emitting device may include a ceramic substrate having a reflective component, a light-emitting diode on the ceramic substrate, and a light-converting material over the light-emitting diode.
One aspect of a lighting system is disclosed. A lighting system may include a ceramic substrate having a reflective component, a plurality of light-emitting diodes connected together in series, wherein the plurality of light-emitting diodes are on the ceramic substrate, and a light-converting material over the plurality of light-emitting diodes.
It is understood that other aspects of apparatuses will become readily apparent to those skilled in the art from the following detailed description, wherein various aspects of apparatuses and methods are shown and described by way of illustration. As understood by one of ordinary skill in the art, these aspects may be implemented in other and different forms and its several details are capable of modification in various other respects. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.
Various aspects of apparatuses will now be presented in the detailed description by way of example, and not by way of limitation, with reference to the accompanying drawings, wherein:
The detailed description set forth below in connection with the appended drawings is intended as a description of various exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring the concepts of the present invention. Acronyms and other descriptive terminology may be used merely for convenience and clarity and are not intended to limit the scope of the invention.
The word “exemplary” is used herein to mean serving as an example, instance, or illustration. Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Likewise, the term “embodiment” of an apparatus, method or article of manufacture does not require that all embodiments of the invention include the described components, structure, features, functionality, processes, advantages, benefits, or modes of operation.
The various aspects of the present invention illustrated in the drawings may not be drawn to scale. Rather, the dimensions of the various features may be expanded or reduced for clarity. In addition, some of the drawings may be simplified for clarity. Thus, the drawings may not depict all of the components of a given apparatus or method. Various aspects of the present invention will be described herein with reference to drawings that are schematic illustrations of idealized configurations of the present invention. As such, variations from the shapes of the illustrations as a result, for example, manufacturing techniques and/or tolerances, are to be expected. Thus, the various aspects of the present invention presented throughout this disclosure should not be construed as limited to the particular shapes of elements (e.g., regions, layers, sections, substrates, bulb shapes, etc.) illustrated and described herein but are to include deviations in shapes that result, for example, from manufacturing. By way of example, an element illustrated or described as a rectangle may have rounded or curved features and/or a gradient concentration at its edges rather than a discrete change from one element to another. Thus, the elements illustrated in the drawings are schematic in nature and their shapes are not intended to illustrate the precise shape of an element and are not intended to limit the scope of the present invention.
It will be understood that when an element such as a region, layer, section, substrate, or the like, is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. It will be further understood that when an element is referred to as being “formed” on another element, it can be grown, deposited, etched, attached, connected, coupled, or otherwise prepared or fabricated on the other element or an intervening element.
It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The term “and/or” includes any and all combinations of one or more of the associated listed items.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by a person having ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
In the following detailed description, various aspects of the present invention will be presented in the context of a light-emitting device. However, those skilled in the art will realize that these aspects may be extended to other apparatus and/or their features, operations, elements, and/or components. Accordingly, any reference to a light-emitting device is intended only to illustrate the various aspects of the present invention, with the understanding that such aspects may have a wide range of applications.
Applicant hereby incorporates by reference the disclosure previously provided in U.S. patent application Ser. No. 12/705,240, filed on Feb. 12, 2010, which is now U.S. Pat. No. 8,371,718.
The area 206 includes an n-type semiconductor region and a p-type semiconductor region. The n-type semiconductor region is predominated by electrons. The p-type semiconductor region is predominated by holes. During operation of the light-emitting diode 202, a reverse electric field is created at the junction between the n-type semiconductor region and the p-type semiconductor region (sometimes referred to herein as the “p-n junction”). The reverse electric field causes the electrons and holes to move away from the p-n junction, thereby forming an active region. When forward voltage sufficient to overcome the reverse electric field is applied across the p-n junction, electrons and holes are forced into the active region and are combined together. When electrons combine with holes, the particles fall to lower energy levels. Falling to lower energy levels causes energy to be released, and the energy released may be in the form of emitted light. Accordingly, power applied to the contacts 204 can cause light to be emitted by the light-emitting diode 202.
The light-emitting diodes 202 may be positioned on top of the ceramic substrate 310. The ceramic substrate 310 may include various materials. In some exemplary embodiments, the ceramic substrate 310 may include silicon (Si). Silicon provides thermal conductivity of approximately 150 W/mK. Accordingly, silicon provides good thermal conductivity. In some exemplary embodiments, the ceramic substrate 310 may include aluminum nitride (AlN). Aluminum nitride provides thermal conductivity of approximately 285 W/mK. Accordingly, aluminum nitride also provides good thermal conductivity. Also, aluminum nitride may provide a band gap (also known as an ‘energy gap’) of approximately 6.2 eV. Accordingly, aluminum nitride has low conductivity efficiency and therefore low electrical conductivity. In some exemplary embodiments, the ceramic substrate 310 may include aluminum oxide (Al2O3).
The foregoing embodiments provide non-limiting examples of materials that may be provided in the ceramic substrate 310 to provide (1) high thermal conductivity and/or (2) low electrical conductivity. High thermal conductivity provides for high rates of heat transfer through the ceramic substrate 310 and, therefore, away from the light-emitting diodes 202. Transfer of heat away from the light-emitting diodes 202 prevents over-heating of the light-emitting diodes 202. Over-heating of the light-emitting diodes 202 may increase the temperature at the p-n junction and thereby decrease the overall performance of the light-emitting diodes 202. Accordingly, the ceramic substrate 310 may provide at least some thermal conductivity between at least one light-emitting diode 202 and the aluminum carrier 314.
Low electrical conductivity prevents power from escaping through the ceramic substrate 310. Power escaping through the ceramic substrate 310 may require additional power to be provided to other light-emitting diodes 202 connected in series, thereby reducing power efficiency of the overall light-emitting device 102. Accordingly, the ceramic substrate 310 may provide at least some electrical insulation between at least one light-emitting diode 202 and the aluminum carrier 314.
The ceramic substrate 310 may also include a reflective component. In some exemplary embodiments, the reflective component includes zirconium oxide (ZrO2). The reflective component (e.g., zirconium oxide) may be infused throughout the ceramic substrate 310. The reflective component may increase the reflective properties of the ceramic substrate 310. Generally, reflectivity refers to the degree to which a material reflects light emitted onto it. The reflectivity of a material may be measured according to a reflectivity index or a percentage of light that reflects when light is emitted onto it. For example, a percent reflectivity of the ceramic substrate 310 having the reflective component may be at least 70%.
The foregoing embodiments provide non-limiting examples of materials that may be provided in the ceramic substrate 310 to provide high reflectivity of light. In
A light-converting material 316 may be provided on the ceramic substrate 310 and/or the light-emitting diodes 202. When light emitted by the light-emitting diodes 202 passes through the light-converting material 316, the color of the light may change. In some embodiments, the light-converting material 316 is phosphor. For example, a layer of phosphor may be provided over the light-emitting diodes 202.
The ceramic substrate may include various materials (e.g., silicon, aluminum nitride, and/or aluminum oxide) that may increase thermal conductivity and/or decrease electrical conductivity of the ceramic substrate 310. Increasing thermal conductivity of the ceramic substrate 310 may increase heat transfer away from the light-emitting diode 202, thereby improving the performance of the light-emitting diode 202. Decreasing electrical conductivity of the ceramic substrate 310 may decrease power loss, thereby improving power efficiency of the light-emitting device 102.
The ceramic substrate 310 may also include a reflective component (e.g., zirconium oxide), which may be infused throughout the ceramic substrate 310. The reflective component may increase the reflectivity of the ceramic substrate 310, which consequently decreases self-absorption, increases conversion efficiency, and increases overall light output. The die attach material 312 may secure the ceramic substrate 310 to the aluminum carrier 314.
One of ordinary skill in the art will appreciate that any description provided with respect to the light-emitting device 102 may also apply to any lighting system, any light-emitting apparatus, and/or any other apparatus that emits light.
Encapsulant 416 can be used to encapsulate and surround electrodes 414 on at least one side. Encapsulant 416 can also provide support to the entire LED device 402 so that LED device 402 is more stable, rigid and does not deform during processing or handling. Encapsulant 416 is a transparent encapsulant that can be formed from a silicone based material. Transparent encapsulant 416 can be cured to become solid. Alternatively, transparent encapsulant 416 can be fabricated using spin-on dielectric materials or spin-on glass materials, which can also be subsequently cured to make solid. In another alternate embodiment, transparent encapsulant 416 is formed using compression molding, transfer molding or injection molding techniques.
During operation, a portion of the light emitted by light emitting layers 410 is scattered by surrounding packaging components used to package the LED device 402. The transparent encapsulant permits the scattered light to pass through with minimal absorption. By using transparent encapsulant 416, the efficiency of a packaged LED device is significantly improved because light is not absorbed by the transparent encapsulant material. For example, in a multi-chip package using transparent encapsulant 416 the efficiency can be between 5% and 10% greater than in a multi-chip package using non-transparent encapsulant.
Encapsulant 416 can be used to encapsulate and surround electrodes 414 and reflective layers 418 on at least one side. Encapsulant 416 can also provide support to the entire LED device 404 so that LED device 404 is more stable, rigid and does not deform during processing or handling. Encapsulant 416 is a transparent encapsulant that can be formed from a silicone based material. Transparent encapsulant 416 can be cured to become solid. Alternatively, transparent encapsulant 416 can be fabricated using spin-on dielectric materials or spin-on glass materials, which can also be subsequently cured to make solid. In another alternate embodiment, transparent encapsulant 416 is formed using compression molding, transfer molding or injection molding techniques.
Reflective layers 418 are used to enhance the efficiency of the packaged LED by reflecting scattered light from the electrodes 414, which would otherwise be partially absorbed by the electrodes 414. Reflective layer is fabricated from aluminum based, titanium oxide or other white or reflective materials. The reflective layer is fabricated on the walls of the electrodes by plating, sputtering, spraying etc. During operation, a portion of the light emitted by light emitting layers 410 is scattered by surrounding packaging components used to package the LED device 404. The transparent encapsulant 416 permits the scattered light to pass through with minimal absorption. The reflective layer 418, which is formed on the electrodes 414, reflects light from electrodes 414 so that electrodes 414 do not absorb the light passing through the encapsulant. Reflective layers 418 enhance the efficiency of the packaged LED device 404. In some embodiments, the efficiency of a packaged LED device 404, which includes both transparent encapsulant 416 and a reflective layer 418 on the electrodes 414, is significantly improved. For example, in a multi-chip package using transparent encapsulant 416 and a reflective layer 418 on the electrodes 414, the efficiency can be greater than 5% to 10% than in a multi-chip package using non-transparent encapsulant.
The various aspects of this disclosure are provided to enable one of ordinary skill in the art to practice the present invention. Various modifications to exemplary embodiments presented throughout this disclosure will be readily apparent to those skilled in the art, and the concepts disclosed herein may be extended to other devices. Thus, the claims are not intended to be limited to the various aspects of this disclosure, but are to be accorded the full scope consistent with the language of the claims. All structural and functional equivalents to the various components of the exemplary embodiments 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. Moreover, nothing disclosed 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 the provisions of 35 U.S.C. §112(f) unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”
