Patent Application
20240162381
The present disclosure relates to light-emitting diode (LED) packages and, more particularly, to using a 3D molded or shaped phosphor in glass cover structure to improve a performance of the LED package.
Solid-state lighting devices such as light-emitting diodes (LEDs) are increasingly used in both consumer and commercial applications. Advancements in LED technology have resulted in highly efficient and mechanically robust light sources with a long service life. Accordingly, modern LEDs have enabled a variety of new display applications and are being increasingly utilized for general illumination applications, often replacing incandescent and fluorescent light sources.
Typically, it is desirable to operate LEDs at the highest light emission efficiency possible, which can be measured by the emission intensity in relation to the output power (i.e., in lumens per watt). A practical goal to enhance emission efficiency is to maximize extraction of light emitted by the active region in the direction of the desired transmission of light. Light extraction and external quantum efficiency of an LED can be limited by a number of factors, including internal reflection. According to the well-understood implications of Snell's law, photons reaching an interface between an LED surface and the surrounding environment or even an internal interface of the LED can be either refracted or internally reflected. If photons are internally reflected in a repeated manner, then such photons are eventually absorbed and never provide visible light that exits an LED.
It is often desirable to incorporate a phosphor into the light emitting device, to enhance the emitted radiation in a particular frequency band and/or to convert at least some of the radiation to another frequency band.
The phosphor can be embedded in a glass cover structure that is bonded to the LED chip or device and can both protect the LED chip/device while also providing an emitted light in a desired frequency band. The phosphor in glass is traditionally flat, however, which can lead to reduced efficiency and impaired color over angle emission due to light entering the phosphor in glass cover structure at high angles.
The art continues to seek improved LEDs and solid-state lighting devices having desirable illumination characteristics capable of overcoming challenges associated with conventional lighting devices.
The present disclosure relates to techniques for providing and fabricating a 3D shaped phosphor in glass cover structure for a light emitting diode (LED) package that has improved light emission efficiencies and color over angle emissions over flat phosphor in glass cover structures. The phosphor in glass cover structure can form a hemispherical dome over an LED chip, so that light incident on the inside surface of the dome will be at a more acute angle which can reduce the internal reflection of light emitted by the LED chip. The phosphor in glass can also serve as a remote phosphor lumiphore, thereby improving color over angle emission and reduce the need for an additional adhesion interface on the LED. The phosphor in glass cover structure can be molded or pressed during a green sheet lamination and sintering process to create the 3D shape. In other embodiments, a phosphor in glass structure can be machined into a desired shape.
In an embodiment, an LED package can include a submount, an LED chip on the submount, and a glass cover structure embedded with a lumiphoric material, wherein an internal surface of the glass cover structure is non-planar, and at least a portion of the glass cover structure is not in contact with the LED chip.
In an embodiment, a method of forming an LED package comprising a glass cover structure can include laminating a plurality of sublayers each embedded with a lumiphoric material. The method can also include pressing the plurality of sublayers into a mold, wherein the plurality of sublayers conform to a predefined shape. The method can also include sintering the sublayers to form a glass cover structure. The method can also include fixing the glass cover structure to the LED package, wherein the glass cover structure covers an LED chip on the LED package.
In another embodiment, a method of forming an LED package comprising a glass cover structure can include laminating a plurality of sublayers each embedded with a lumiphoric material. The method can also include sintering the sublayers to form a glass block. The method can also include machining the glass block to form a glass cover structure having a hemispherical dome shape. The method can also include fixing the glass cover structure to the LED package, wherein the glass cover structure covers an LED chip on the LED package.
In another aspect, any of the foregoing aspects individually or together, and/or various separate aspects and features as described herein, may be combined for additional advantage. Any of the various features and elements as disclosed herein may be combined with one or more other disclosed features and elements unless indicated to the contrary herein.
Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.
The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.
technique for fabricating a 3D shaped phosphor in glass cover structure according to one or more aspects of the present disclosure.
The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.
Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, 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.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Embodiments are described herein with reference to schematic illustrations of embodiments of the disclosure. As such, the actual dimensions of the layers and elements can be different, and variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are expected. For example, a region illustrated or described as square or rectangular can have rounded or curved features, and regions shown as straight lines may have some irregularity. Thus, the regions illustrated in the figures are schematic and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the disclosure. Additionally, sizes of structures or regions may be exaggerated relative to other structures or regions for illustrative purposes and, thus, are provided to illustrate the general structures of the present subject matter and may or may not be drawn to scale. Common elements between figures may be shown herein with common element numbers and may not be subsequently redescribed.
The present disclosure relates to techniques for providing and fabricating a 3D shaped phosphor in glass (PiG) cover structure for a light emitting diode (LED) package that has improved light emission efficiencies and color over angle emissions over flat PiG cover structures. The PiG cover structure can form a hemispherical dome over an LED chip, so that light incident on the inside surface of the dome will be at a more acute angle which can reduce the internal reflection of light emitted by the LED chip. The PiG can also serve as a remote phosphor lumiphore, thereby improving color over angle emission and reduce the need for an additional adhesion interface on the LED. The PiG cover structure can be molded or pressed during a green sheet lamination and sintering process to create the 3D shape. In other embodiments, a PiG structure can be machined into a desired shape.
Before delving into specific details of various aspects of the present disclosure, an overview of various elements that may be included in exemplary LED packages of the present disclosure is provided for context. An LED chip typically comprises an active LED structure or region that can have many different semiconductor layers arranged in different ways. The fabrication and operation of LEDs and their active structures are generally known in the art and are only briefly discussed herein. The layers of the active LED structure can be fabricated using known processes with a suitable process being fabrication using metal organic chemical vapor deposition. The layers of the active LED structure can comprise many different layers and generally comprise an active layer sandwiched between n-type and p-type oppositely doped epitaxial layers, all of which are formed successively on a growth substrate. It is understood that additional layers and elements can also be included in the active LED structure, including, but not limited to, buffer layers, nucleation layers, super lattice structures, undoped layers, cladding layers, contact layers, and current-spreading layers and light extraction layers and elements. The active layer can comprise a single quantum well, a multiple quantum well, a double heterostructure, or super lattice structures.
The active LED structure can be fabricated from different material systems, with some material systems being Group III nitride-based material systems. Group III nitrides refer to those semiconductor compounds formed between nitrogen (N) and the elements in Group III of the periodic table, usually aluminum (Al), gallium (Ga), and indium (In). Gallium nitride (GaN) is a common binary compound. Group III nitrides also refer to ternary and quaternary compounds such as aluminum gallium nitride (AIGaN), indium gallium nitride (InGaN), and aluminum indium gallium nitride (AlInGaN). For Group III nitrides, silicon (Si) is a common n-type dopant and magnesium (Mg) is a common p-type dopant. Accordingly, the active layer, n-type layer, and p-type layer may include one or more layers of GaN, AIGaN, InGaN, and AlInGaN that are either undoped or doped with Si or Mg for a material system based on Group III nitrides. Other material systems include silicon carbide (SiC), organic semiconductor materials, and other Group III-V systems such as gallium phosphide (GaP), gallium arsenide (GaAs), and related compounds.
The active LED structure may be grown on a growth substrate that can include many materials, such as sapphire, SiC, aluminum nitride (AIN), GaN, with a suitable substrate being a 4H polytype of SiC, although other SiC polytypes can also be used including 3C, 6H, and 15R polytypes. SiC has certain advantages, such as a closer crystal lattice match to Group III nitrides than other substrates and results in Group III nitride films of high quality. SiC also has a very high thermal conductivity so that the total output power of Group III nitride devices on SiC is not limited by the thermal dissipation of the substrate. Sapphire is another common substrate for Group III nitrides and also has certain advantages, including being lower cost, having established manufacturing processes, and having good light transmissive optical properties.
Different embodiments of the active LED structure can emit different wavelengths of light depending on the composition of the active layer and n-type and p-type layers. In certain embodiments, the active LED structure may emit blue light with a peak wavelength range of approximately 430 nanometers (nm) to 480 nm. In other embodiments, the active LED structure may emit green light with a peak wavelength range of 500 nm to 570 nm. In other embodiments, the active LED structure may emit red light with a peak wavelength range of 600 nm to 650 nm. In certain embodiments, the active LED structure may emit light with a peak wavelength in any area of the visible spectrum, for example, peak wavelengths primarily in a range from 400 nm to 700 nm.
In certain embodiments, the active LED structure may be configured to emit light that is outside the visible spectrum, including one or more portions of the ultraviolet (UV) spectrum, the infrared (IR) or near-IR spectrum. The UV spectrum is typically divided into three wavelength range categories denoted with letters A, B, and C. In this manner, UV-A light is typically defined as a peak wavelength range from 315 nm to 400 nm, UV-B is typically defined as a peak wavelength range from 280 nm to 315 nm, and UV-C is typically defined as a peak wavelength range from 100 nm to 280 nm. UV LEDs are of particular interest for use in applications related to the disinfection of microorganisms in air, water, and surfaces, among others. In other applications, UV LEDs may also be provided with one or more lumiphoric materials to provide LED packages with aggregated emissions having a broad spectrum and improved color quality for visible light applications. Near-IR and/or IR wavelengths for LED structures of the present disclosure may have wavelengths above 700 nm, such as in a range from 750 nm to 1100 nm, or more.
The LED chip can also be covered with one or more lumiphoric or other conversion materials, such as phosphors, such that at least some of the light from the LED chip is absorbed by the one or more phosphors and is converted to one or more different wavelength spectra according to the characteristic emission from the one or more phosphors. In some embodiments, the combination of the LED chip and the one or more phosphors emits a generally white combination of light. The one or more phosphors may include yellow (e.g., YAG:Ce), green (e.g., LuAg:Ce), and red (e.g., Cai-x-ySrxEuyAlSiN3) emitting phosphors, and combinations thereof. Lumiphoric materials as described herein may be or include one or more of a phosphor, a scintillator, a lumiphoric ink, a quantum dot material, a day glow tape, and the like. In certain embodiments, lumiphoric materials may be downconverting or upconverting, and combinations of both downconverting and upconverting materials may be provided. In certain embodiments, multiple different (e.g., compositionally different) lumiphoric materials arranged to produce different peak wavelengths may be arranged to receive emissions from one or more LED chips. In some embodiments, one or more phosphors may include yellow phosphor (e.g., YAG:Ce), green phosphor (e.g., LuAg:Ce), and red phosphor (e.g., Cai-x-ySrxEuyAlSiN3) and combinations thereof. One or more lumiphoric materials may be provided on one or more portions of an LED chip and/or a submount in various configurations. In certain embodiments, the loading percentage of one or more lumiphoric materials may be varied relative to one or more outer surfaces of an LED chip. In certain embodiments, one or more lumiphoric materials may be patterned to include one or more stripes, dots, curves, or polygonal shapes. In certain embodiments, multiple lumiphoric materials may be arranged in different discrete regions or discrete layers relative to an LED chip.
Aspects of the present disclosure are provided that include optical arrangements for cover structures of LED packages for improving or otherwise tailoring emission characteristics. Such cover structures may include hard and mechanically robust structures that are positioned over one or more LED chips within an LED package. A cover structure may be configured to provide protection from environmental exposure to underlying portions of an LED package, thereby providing a more robust LED package that is well suited for applications that require high power with increased light intensity, contrast, and reliability, such as interior and exterior automotive applications. Cover structures may comprise host materials such as glass or ceramics that provide mechanically robust structures for environmental protection. Such cover structures may be fabricated by providing sheets of glass frit or ceramic precursor materials, pressing the sheets into planar shapes, and firing or sintering to form hardened structures that can be cut or separated. The resulting cover structure may be referred to as a glass plate or a ceramic plate. When lumiphoric materials, such as phosphors, are included in the glass frit or ceramic precursor materials, the resulting cover structures may be referred to as phosphor in glass (PiG) plates or ceramic phosphor plates. In an embodiment, a transparent ceramic cover structure could be sprayed with a phosphor and silicone mixture to generate a remote phosphor with improved emission characteristics. Conventional phosphor can tend to exhibit non-uniformity of emissions due to poor color over angle for light that is converted. It is to be appreciated herein that when a 3D shaped PiG cover structure or PiG cover structure is referred to, that in different embodiments, the cover structure could be a transparent ceramic cover structure.
The conventional plates have traditionally been planar, and have had at least several drawbacks. The first drawback is that the planar plates have been bonded to the LED chips using an adhesive layer and the adhesive layer can absorb at least some of the light emitted by the LED chip thus reducing the overall transmission efficiency. Another drawback is that a substantial portion of the light incident on the planar plates is at an angle such that reflection and refraction both reduce the transmission efficiency and impair the color over angle emission of the LED device. The 3D shaped PiG cover structure disclosed herein overcomes these drawbacks.
The 3D shaped PiG is also an improvement over 3D shaped plastic shells that may have phosphor embedded in the plastic shell. With the phosphor embedded in glass, and not plastic, there are index of refraction improvements that improve color over angle emissions. Additionally, glass has improved thermal characteristics relative to plastic, and can handle high and low temperatures without becoming brittle. Furthermore, glass does not discolor over time due to ultraviolet radiation or other gases as does plastic. Previously shaping the glass in the desired shape was difficult, but the methods of fabrication disclosed herein by heating and pressing green sheets have overcome the challenges of using PiGs.
In an embodiment, the PiG cover structure 102 can form the LED package 100 along with a submount 104, and LED chip 106 mounted to the submount 104. In an embodiment, the submount 104 can extend beyond the edges of the LED chip 106 and the PiG cover structure 102 can be mounted to the submount 104. It is to be appreciated that the
In an embodiment, the PiG cover structure 102 can be a hemispherical dome shape. In other embodiments, the PiG cover structure can take other shapes with curves or facets. In the various embodiments however, the PiG cover structure 102 can be shaped such that light (e.g., 110, and 112) incident on an internal surface 108 of the PiG cover structure 102 forms an acute angle with respect to a normal axis 114 of the internal surface 108 of the PiG cover structure 102.
In an embodiment, the color of the light that exits the PiG cover structure 102 can be more uniform than if the PiG cover structure 102 were flat as the light passes through the PiG cover structure 102 more directly. When light passes through PiG, light that enters at high angles can encounter more phosphor than light that passes through at an acute angle, which can result in yellower emission near the edges of the flat PiG cover structure.
In an embodiment, the 3D shaped PiG cover structure 102 can serve as a remote phosphor lumiphore, which can improve the color over angle emission by ensuring light passes through the PiG cover structure 102 more uniformly. Additionally, by mounting the PiG cover structure 102 to the submount 104, the light (e.g., 110 and 112) does not pass through an adhesive layer that would have attached the PiG cover structure to the LED chip. The adhesive layer can block some of the light, and so having the PiG cover structure 102 be mounted to the submount 104, transmission efficiency is increased by removing the adhesive layer. In another embodiment, by having the PiG cover structure 102 be at a distance from the LED chip 106 and not touching the LED chip 106, the PiG cover structure 102 is thermally insulated to a degree, and is cooler than the PiG cover structure 102 would be if it were in contact with the LED chip 106. Since transmission efficiency decreases at increased temperatures, the transmission efficiency remains high for PiG cover structure 102.
In an embodiment, the 3D shaped PiG cover structure 102 can be used in applications such as bulbs where a large emission angle is desired, such as bulbs with a 180 ° emission range. In other embodiments, the PiG cover structure 102 can be tuned to help control not color vs angle emission but also intensity vs angle emission, where a desired intensity at predefined angles can be configured.
In
In the embodiment in
In an embodiment depicted in
In an embodiment, the green sheets 406 (e.g., 406-1, 406-2, and 406-3) can be placed between a shaped press 504 and mold 506 in
Once the PiG has reached the predetermined temperature, the press 504 can be pressed into the mold 506 as shown in
In an alternative embodiment, the heating and pressing performed in
In
The press 604 in
Once the intermediate PiG structure 602 has been singulated, a machining tool 608 can machine the intermediate PiG structure 602 into a hemispherical dome in
In an embodiment, the heating and pressing performed in
Alternatively, as shown in
The method can begin at step 902 where the method includes laminating a plurality of sublayers each comprising a lumiphoric material. In one or more embodiments, the lumiphoric material can be phosphor.
At step 904, the method includes pressing the plurality of sublayers into a mold, wherein the plurality of sublayers conform to a predefined shape. In an embodiment, the predefined shape can be a hemispherical dome. In other embodiments, the predefined shape can have a plurality of planar facets. The predefined shape can be such that when light is incident on an internal surface of the glass cover structure the light is at an acute angle relative to an axis normal to the internal surface of the shape.
At step 906, the method includes sintering the sublayers to form a glass cover structure.
At step 908, the method includes fixing the glass cover structure to the LED package, wherein the glass cover structure covers an LED chip on the LED package. The glass cover structure can be mounted to a submount in some embodiments, or directly to the LED chip of the LED package in other embodiments. In an embodiment where the glass cover structure is mounted to the submount, the glass cover structure can serve as a remote phosphor lumiphore, thereby improving color over angle emission and reducing the need for an additional adhesion interface on the LED.
The method can begin at step 1002 where the method includes laminating a plurality of sublayers each comprising a lumiphoric material. In one or more embodiments, the lumiphoric material can be phosphor
At step 1004, the method includes sintering the sublayers to form a phosphor in glass structure.
At step 1006, the method includes machining the phosphor in glass structure to form a glass cover structure having a hemispherical dome shape. In an embodiment, the hemispherical dome shape can be such that when light is incident on an internal surface of the glass cover structure the light is at an acute angle relative to an axis normal to the internal surface of the glass cover structure.
At step 1008, the method includes fixing the glass cover structure to the LED package, wherein the glass cover structure covers an LED chip on the LED package. The glass cover structure can be mounted to a submount in some embodiments, or directly to the LED chip of the LED package in other embodiments. In an embodiment where the glass cover structure is mounted to the submount, the glass cover structure can serve as a remote phosphor lumiphore, thereby improving color over angle emission and reducing the need for an additional adhesion interface on the LED.
It is contemplated that any of the foregoing aspects, and/or various separate aspects and features as described herein, may be combined for additional advantage. Any of the various embodiments as disclosed herein may be combined with one or more other disclosed embodiments unless indicated to the contrary herein.
Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.
