DISCRETE PHOSPHOR CHIPS FOR LIGHT-EMITTING DEVICES AND RELATED METHODS
In accordance with certain embodiments, phosphor chips are formed and subsequently attached to light-emitting elements.
This application claims the benefit of and priority to U.S. Provisional Patent Application No. 61/589,908, filed Jan. 24, 2012, and U.S. Provisional Patent Application No. 61/589,909, filed Jan. 24, 2012, the entire disclosure of each of which is hereby incorporated herein by reference.
FIELD OF THE INVENTIONIn various embodiments, the present invention generally relates to light sources, and more specifically to phosphor-converted light sources.
BACKGROUNDLight sources such as light-emitting diodes (LEDs) are an attractive alternative to incandescent and fluorescent light bulbs in illumination devices due to their higher efficiency, smaller form factor, longer lifetime, and enhanced mechanical robustness. However, the high cost of LED-based lighting systems has limited their widespread utilization, particularly in broad-area general lighting applications.
The high cost of LED-based lighting systems has several contributors. LEDs are typically encased in a package, and multiple packaged LEDs are used in each lighting system to achieve the desired light intensity. For general illumination, which utilizes white light, such white light may be generated in a number of ways. One approach is to utilize two or more LEDs operating at different wavelengths, where the different wavelengths combine to appear white to the human eye. For example, LEDs emitting in the red, green and blue wavelength ranges may be utilized together. Such an arrangement typically requires careful control of the operating currents of each LED, such that the resulting combination of wavelengths is stable over time and different operating conditions, for example temperature. The different LEDs may also be formed of different materials, for example, AlInGaP for red LEDs and AlInGaN for blue and green LEDs. These different materials may have different operating current requirements as well as different temperature dependencies of the light output power and wavelength. Furthermore, changes in light-output power with time may be different for each type of LED. Therefore, such systems typically utilize some form of active control of the current in each LED to maintain the light output power of each LED at the desired level. In some implementations one or more sensors (for example to sense light intensity, light color, temperature or the like) may be used to provide feedback to the current-control system, while in some other implementations the current may be adjusted over time based on values in a look-up table. Such control systems add cost and complexity to lighting solutions, as well as creating additional failure points. A further disadvantage of multi-LED arrangements is that they typically require some form of light combiner, diffuser or mixing chamber, so that the eye observes white light rather than the discrete different colors of each of the different LEDs. Such light-mixing systems typically add cost and bulk to lighting systems as well as reducing their efficiency.
White light may also be produced in LED-based arrangements for general illumination by means of light-conversion materials such as phosphors. LEDs generally emit in a relatively narrow wavelength range, for example on the order of about 20-100 nm. When broader spectra (for example “white” light) or colors different from that of the LED are desired, the LED may be combined with one or more light-conversion materials. An LED combined with one or more phosphors typically generates white light by combining the short-wavelength emission from the semiconductor LED with long-wavelength emission from the phosphor(s). This occurs because a portion of the LED light passes unconverted through the phosphor to combine with the phosphor-converted light. Phosphors are typically composed of phosphorescent particles such as Y3Al5O12:Ce3+ (cerium-activated yttrium-aluminum-garnet, or YAG:Ce) embedded in a transparent binder such as optical epoxy or silicone and applied as a layer.
In some implementations, the white light is a combination of the light emitted by the light emitter and the phosphor, while in other implementations the white light is substantially emitted by the phosphor alone (in this case the light from the light emitter is substantially not visible directly by the viewer). Herein, “white light” may be white or any other color that is produced by a combination of light from one or more light emitters and one or more light-conversion materials.
In some implementations, the phosphor layer absorbs a portion of the incident short-wavelength radiant flux and re-emits long-wavelength radiant flux. For an exemplary YAG:Ce phosphor, a blue LED may have a peak wavelength of 450 nm-460 nm, corresponding to the peak of the phosphor-excitation spectrum, while the phosphor emission has a broadband spectrum with a peak at approximately 560 nm. Combining the blue LED emission with the yellow phosphor emission yields visible white light with a specific chromaticity (color) that depends on the ratio of blue light to yellow light.
The geometry of the phosphor relative to the LED generally has a very strong impact on the uniformity of the resulting light. For example, the LED may emit from both the surface and the sides of the LED, producing non-uniform color if the phosphor composition is not uniform over these LED surfaces. To combat this problem, the LED may be placed in a reflecting cavity covered by a wavelength-converting ceramic, with the gap between the LED and the converter optionally filled with a transparent material, such that all of the light from the LED exits the cavity through the converter. However, ceramic wavelength converters may be difficult to manufacture and brittle in thin-film form. Furthermore, they may be expensive to integrate in arrays of small LEDs.
If the thickness of the phosphor layer, formed of a uniformly dispersed phosphor in a binder, is not uniform over the surface of the LED, relatively larger amounts of blue light will be present where the phosphor-infused binder layer is thinner and relatively smaller amounts of blue light will be present where the phosphor-infused binder is thicker. While techniques such as electrophoresis may be utilized to produce a uniform phosphor coating on an LED, electrophoresis typically requires a conductive substrate or an electrically conductive coating, thus increasing cost and complexity.
Phosphor integration typically takes two forms. In one approach the phosphor is integrated in the LED package along with the LED die, while in the other the phosphor is separate from the LED package or LED die. Packaged phosphor-converted LEDs, also known as packaged white LEDs, are typically fabricated by mounting the LED die on a portion of the package followed by integration of the phosphor. In some implementations, the phosphor is mixed with a binder or encapsulant formed over the mounted LED die and optionally over other portions of the package. It is desirable to be able to produce packaged white LEDs with relatively narrow distributions of electrical and optical characteristics, for example forward voltage, luminous flux, luminous efficacy, color temperature, color rendering index (CRI) and the like. However, there is a relatively large variation in these characteristics for the LED dies themselves due to the growth process for the epitaxial structure and the fabrication process of the LED dies. This variation is difficult to reduce, resulting in the need to test, sort and bin the LED dies for almost all applications. In other words, all of the LED dies are tested and grouped into bins related, typically, to forward voltage, light output power and wavelength. LED dies from specific bins are then chosen, based on the requirements of the particular application, put into a package, followed by formation of the phosphor around all or a portion of the LED die.
As explained above, in order to produce uniform optical properties from the packaged white LEDs, the phosphor process typically must be relatively uniform. In some implementations the phosphor, which is typically a powder, is mixed in a liquid binder and applied to the LED dies. It may be difficult to form a uniform layer of phosphor over the LED dies, resulting in different color temperatures for different packaged white LEDs. Furthermore, the phosphor powder typically has a significantly higher density than the binder, leading to settling of the phosphor powder during manufacture and a resulting variation in color temperature. In practice, packaged white LEDs are tested after manufacture and sorted and binned to produce groups of packaged white LEDs with uniform electrical and optical characteristics. It is clear that this is a complicated and costly process, with the potential for a significant portion of the output having non-optimal characteristics.
Conventional approaches may suffer from heating of the phosphor because the phosphor is in relatively good thermal contact with the LED die. As the phosphor heats up, it may lose efficiency and shift its optical properties, both of which are undesirable. One approach to at least partially mitigating heating of the phosphor is to provide increased thermal separation of the phosphor from the LED. Such an approach is sometimes called a “remote phosphor.” Remote phosphor configurations may be incorporated into packaged white LEDs by providing some physical and/or thermal separation of the phosphor from the LED die. One approach is to insert a portion of transparent binder or encapsulant between the phosphor-containing binder and the LED die. While such approaches at least partially mitigate phosphor heating, they result in a more complex and costly structure.
These issues may apply to many types of phosphor-converted light emitters, including single die-packaged devices, multiple die-packaged devices, arrays of packaged LEDs and single or arrays of unpackaged dies to which phosphor is applied.
In view of the foregoing, a need exists for structures, systems and procedures enabling the uniform and low cost integration of phosphors with LEDs.
SUMMARYIn accordance with certain embodiments, phosphor is molded, cured, and, if necessary, divided into free-standing solid portions (or “phosphor chips”) that are subsequently attached to light-emitting elements (LEEs) so as to receive light emitted by the LEEs. The molding process enables fabrication of phosphor chips having very low thickness variation. These chips may be textured (for example, to increase light-extraction efficiency), and/or may be rectangular solids. The molding process may be utilized to fabricate multiple phosphor chips simultaneously, either via use of a mold having discrete areas for containing the phosphor or by separating a larger piece of cured phosphor into multiple pieces of desired sizes and shapes.
As utilized herein, the term “light-emitting element” (LEE) refers to any device that emits electromagnetic radiation within a wavelength regime of interest, for example, visible, infrared or ultraviolet regime, when activated, by applying a potential difference across the device or passing a current through the device. Examples of LEEs include solid-state, organic, polymer, phosphor-coated or high-flux LEDs, microLEDs (described below), laser diodes or other similar devices as would be readily understood. The emitted radiation of a LEE may be visible, such as red, blue or green, or invisible, such as infrared or ultraviolet. A LEE may produce radiation of a spread of wavelengths. A LEE may feature a phosphorescent or fluorescent material for converting a portion of its emissions from one set of wavelengths to another. A LEE may include multiple LEEs, each emitting essentially the same or different wavelengths. In some embodiments, a LEE is an LED that may feature a reflector over all or a portion of its surface upon which electrical contacts are positioned. The reflector may also be formed over all or a portion of the contacts themselves. In some embodiments, the contacts are themselves reflective.
A LEE may be of any size. In some embodiments, a LEEs has one lateral dimension less than 500 μm, while in other embodiments a LEE has one lateral dimension greater than 500 μm. Exemplary sizes of a relatively small LEE may include about 175 μm by about 250 μm, about 250 μm by about 400 μm, about 250 μm by about 300 μm, or about 225 μm by about 175 μm. Exemplary sizes of a relatively large LEE may include about 1000 μm by about 1000 μm, about 500 μm by about 500 μm, about 250 μm by about 600 μm, or about 1500 μm by about 1500 μm. In some embodiments, a LEE includes or consists essentially of a small LED die, also referred to as a “microLED.” A microLED generally has one lateral dimension less than about 300 μm. In some embodiments, the LEE has one lateral dimension less than about 200 μm or even less than about 100 μm. For example, a microLED may have a size of about 225 μm by about 175 μm or about 150 μm by about 100 μm or about 150 μm by about 50 μm. In some embodiments, the surface area of the top surface of a microLED is less than 50,000 μm2 or less than 10,000 μm2. The size of the LEE is not a limitation of the present invention.
As used herein, “phosphor” refers to any material that shifts the wavelengths of light irradiating it and/or that is fluorescent and/or phosphorescent, and is utilized interchangeably with the term “light-conversion material.” As used herein, a “phosphor” may refer to only the powder or particles (of one or more different types) or to the powder or particles with the binder. The light-conversion material is incorporated to shift one or more wavelengths of at least a portion of the light emitted by LEEs to other desired wavelengths (which are then emitted from the larger device alone or color-mixed with another portion of the original light emitted by the die). A light-conversion material may include or consist essentially of phosphor powders, quantum dots or the like within a transparent matrix. Phosphors are typically available in the form of powders or particles, and in such case may be mixed in binders. An exemplary binder is silicone, i.e., polyorganosiloxane, which is most commonly polydimethylsiloxane (PDMS). Phosphors vary in composition, and may include lutetium aluminum garnet (LuAG or GAL), yttrium aluminum garnet (YAG) or other phosphors known in the art. GAL, LuAG, YAG and other materials may be doped with various materials including for example Ce, Eu, etc. The specific components and/or formulation of the phosphor and/or matrix material are not limitations of the present invention. As used herein, a “phosphor chip” is a discrete piece or layer of phosphor that has been fabricated and cured while unattached to any LEE, and that may be later coupled to an LEE by, e.g., optical bonding or via an optical adhesive.
The binder may also be referred to as an encapsulant or a matrix material. In one embodiment, the binder includes or consists essentially of a transparent material, for example silicone-based materials or epoxy, having an index of refraction greater than 1.35. In one embodiment the phosphor includes or consists essentially of other materials, for example fumed silica or alumina, to achieve other properties, for example to scatter light, or to reduce settling of the powder in the binder. An example of the binder material includes materials from the ASP series of silicone phenyls manufactured by Shin Etsu, or the Sylgard series manufactured by Dow Corning.
Herein, two components such as light-emitting elements, optical elements, and/or phosphor chips being “aligned” or “associated” with each other may refer to such components being mechanically and/or optically aligned. By “mechanically aligned” is meant coaxial or situated along a parallel axis. By “optically aligned” is meant that at least some light (or other electromagnetic signal) emitted by or passing through one component passes through and/or is emitted by the other.
In an aspect, embodiments of the invention feature an electronic device that includes or consists essentially of a substrate having a plurality of conductive traces on a surface thereof, a plurality of light-emitting diode (LED) dies, and a plurality of discrete phosphor chips each disposed over an LED die and positioned to receive light therefrom. Each pair of conductive traces is separated on the substrate by a gap therebetween. Each LED die spans a gap between conductive traces and has first and second spaced-apart contacts each electrically coupled to one of the conductive traces defining the gap. (As used herein, a “gap” is a space between traces sufficient to prevent shorting between the traces.) Each phosphor chip is attached to an LED die by an attachment agent discrete from the LED die and the phosphor chip. Each phosphor chip includes or consists essentially of (i) a light-conversion material and (ii) a binder including or consisting essentially of silicone and/or epoxy.
Embodiments of the invention feature one or more of the following features in any of a variety of combinations. The attachment agent may include or consist essentially of a clip and/or a frame attached to the substrate. The attachment agent may include or consist essentially of an adhesion agent adhering the phosphor chip to the LED die. The transmittance of the attachment agent for a wavelength emitted by the LED die may be greater than 90%, or even greater than 95%. The adhesion agent may include or consist essentially of a transfer tape.
The variation in the thicknesses of the phosphor chip (i.e., chip to chip) may be less than ±5%. Each phosphor chip may absorb at least a portion of light emitted from the LED die over which it is disposed and emit converted light having a different wavelength, and the converted light and unconverted light emitted by the LED die may combine to form substantially white light. The substantially white light emitted collectively from the different LED dies and phosphor chips may have a color temperature variation less than four, or even less than two, MacAdam ellipses. The device may include circuitry for powering at least one LED die and/or circuitry for controlling optical output characteristics (e.g., chromaticity, luminous flux, correlated color temperature, color point, and/or color rendering index) of at least one LED die and the phosphor chip disposed thereover. An optical element may be associated with at least one LED die. The first and second contacts may be electrically coupled to conductive traces with a conductive adhesive (e.g., an anisotropic conductive adhesive (ACA)). The ACA may be disposed between the LED die and the substrate, and the ACA may electrically connect a first conductive trace only to the first contact and a second conductive trace, different from the first conductive trace, only to the second contact. A portion of the ACA may be disposed in the gap and may substantially electrically isolate the first contact from the second contact.
The first and second contacts may be electrically coupled to conductive traces with wire bonds and/or solder. Each LED die may include or consist essentially of a bare LED die. The light-conversion material may include or consist essentially of a plurality of phosphor particles. A surface of the phosphor chip may be textured. The phosphor chip may define an indentation into which the LED die is at least partially disposed. The conductive traces may include or consist essentially of silver, gold, aluminum, chromium, copper, and/or carbon. The substrate may include or consist essentially of polyethylene naphthalate, polyethylene terephthalate, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, and/or paper. The reflectivity of the substrate for a wavelength emitted by the LED die and/or the phosphor chip may be greater than 80%. The transmittance of the substrate for a wavelength emitted by the LED die and/or the phosphor chip may be greater than 80%. The LED die may include or consist essentially of a semiconductor material including or consisting essentially of GaN, AlN, InN, and/or an alloy or mixture thereof.
In another aspect, embodiments of the invention feature an electronic device including or consisting essentially of a light-emitting element and a phosphor chip disposed over the light emitting element and positioned to receive light therefrom. The phosphor chip is attached to the light-emitting element by an attachment agent discrete from the light-emitting element and the phosphor chip. The phosphor chip includes or consists essentially of (i) a light-conversion material and (ii) a binder including or consisting essentially of silicone and/or epoxy.
Embodiments of the invention feature one or more of the following features in any of a variety of combinations. The light-emitting element may be disposed over (and even attached to) a substrate. The attachment agent may include or consist essentially of a clip and/or a frame attached to the substrate. The attachment agent may include or consist essentially of an adhesion agent adhering the phosphor chip to the light-emitting element. The transmittance of the attachment agent for a wavelength emitted by the light-emitting element may be greater than 90%, or even greater than 95%. The adhesion agent may include or consist essentially of a transfer tape.
The phosphor chip may be a rectangular solid having a thickness between 5 μm and 1000 μm. A dimension of the phosphor chip perpendicular to the thickness may be between 100 μm and 5000 μm. The thickness uniformity across the phosphor chip may be better than ±10%, or even better than ±5%. A surface of the phosphor chip may be textured (e.g., roughened). The phosphor chip may define an indentation into which the light-emitting element is at least partially disposed. The device may include a substrate having first and second conductive traces on a surface thereof and separated by a gap therebetween. The light-emitting element may have first and second spaced-apart contacts each electrically coupled to one of the first or second conductive traces. The first and second contacts may both be disposed on a first surface of the light-emitting element. The first and second contacts may be electrically coupled to the first and second conductive traces with a conductive adhesive. The conductive adhesive may include or consist essentially of a substantially isotropic adhesive electrically connecting the first contact only to the first trace and the second contact only to the second trace, and a non-conductive adhesive material may be disposed in the gap. The first and second contacts may be electrically coupled to the first and second conductive traces with an anisotropic conductive adhesive (ACA) electrically connecting the first contact only to the first trace and the second contact only to the second trace. A portion of the ACA may be disposed in the gap and may substantially electrically isolate the first contact from the second contact. The first and second contacts may be electrically coupled to the first and second conductive traces with wire bonds and/or solder. The first and second conductive traces may include or consist essentially of silver, gold, aluminum, chromium, copper, and/or carbon. The substrate may include or consist essentially of polyethylene naphthalate, polyethylene terephthalate, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, and/or paper. The reflectivity of the substrate for a wavelength emitted by the light-emitting element and/or the phosphor chip may be greater than 80%. The transmittance of the substrate for a wavelength emitted by the light-emitting element and/or the phosphor chip may be greater than 80%.
The phosphor chip may include a plurality of discrete regions, at least one of which includes or consists essentially of the binder and a plurality of phosphor particles. At least one portion may include or consist essentially of only the binder. The light-emitting element may include or consist essentially of a semiconductor material including or consisting essentially of GaN, AlN, InN, and/or an alloy or mixture thereof. The light-emitting element may include or consist essentially of a light-emitting diode. The phosphor chip may have a curved shape.
The electronic device may include one or more additional light-emitting elements and one or more additional phosphor chips each disposed over an additional light-emitting element and positioned to receive light therefrom. The phosphor chip and each additional phosphor chip may each have a thickness, and the variation in the thicknesses of the phosphor chips may be less than ±15%, less than ±10%, or even less than ±5%. Each phosphor chip may absorb at least a portion of light emitted from the light-emitting element over which it is disposed and may emit converted light having a different wavelength, converted light and unconverted light emitted by the light-emitting element combining to form substantially white light. The substantially white light may have a color temperature in the range of 2000K to 10,000K. The substantially white light emitted collectively from the different light-emitting elements and phosphor chips may have a color temperature variation less than four, or even less than two, MacAdam ellipses. The device may include circuitry for powering the light-emitting element and/or circuitry for controlling optical output characteristics (e.g., chromaticity, luminous flux, correlated color temperature, color point, and/or color rendering index) of the light-emitting element and the phosphor chip. An optical element may be associated with the light-emitting element.
In yet another aspect, embodiments of the invention feature a method of forming an illumination system that includes or consists essentially of disposing within a mold a phosphor comprising a binder and a light-conversion material, curing the phosphor, thereafter, removing the cured phosphor from the mold, and attaching at least a portion of the cured phosphor to a light-emitting element, whereby the at least a portion of the cured phosphor is positioned to receive light from the light-emitting element.
Embodiments of the invention feature one or more of the following features in any of a variety of combinations. The at least a portion of the cured phosphor may be attached to the light-emitting element with an attachment agent discrete from the light-emitting element and the cured phosphor. The light-emitting element may be attached to a substrate (e.g., via an adhesive, solder, or wire bonds). The attachment agent may include or consist essentially of a clip and/or a frame attached to the substrate. The attachment agent may include or consist essentially of an adhesion agent (e.g., an adhesive) adhering the at least a portion of the cured phosphor to the light-emitting element. Attaching the at least a portion of the cured phosphor to the light-emitting element may include or consist essentially of (i) applying a first portion of the adhesion agent to the light-emitting element, (ii) applying a second portion of the adhesion agent, chemically different from the first portion, to the at least a portion of the cured phosphor, and (iii) bringing the first and second portions of the adhesion agent into contact. The adhesion agent may be at least partially cured via exposure to at least one of ultraviolet radiation, moisture, air, or heat. The adhesion agent may include or consist essentially of a transfer tape. The transmittance of the adhesion agent for a wavelength emitted by the light-emitting element may be greater than 90%, or even greater than 95%.
Prior to curing the phosphor, a mold cover may be placed over the phosphor. The bottom surface of the mold cover may be substantially parallel to a surface of the mold on which the phosphor is disposed. The mold and the mold cover may collectively define a closed cavity (which may be rectilinear) in which the phosphor is disposed. The cured phosphor may be a rectangular solid having a thickness between 5 μm and 1000 μm. A dimension of the cured phosphor perpendicular to the thickness may be between 10 mm and 1000 mm. The thickness uniformity of the cured phosphor may be better than ±15%, better than ±10%, or even better than ±5%. The mold cover may have include at least one opening therein for permitting flow of uncured phosphor therethrough. A release material (e.g., a release film) may be disposed between the phosphor and at least one of (i) at least a portion of the mold or (ii) at least a portion of the mold cover. At least a portion of the mold and/or at least a portion of the mold cover may be textured. A release material (e.g., a release film) may be disposed between the phosphor and at least a portion of the mold. The release material may include or consist essentially of a mold release film applied to the phosphor and/or the at least a portion of the mold, and/or the release material may be textured.
The mold may include or consist essentially of glass, metal, silicone, thermal release tape, water-soluble tape, mold release film, and/or UV release tape. The light-emitting element may have first and second spaced-apart contacts. The first and second contacts may be electrically coupled to first and second conductive traces on a substrate, the first and second conductive traces being separated on the substrate by a gap therebetween. The first and second contacts may be electrically coupled to the first and second conductive traces with a conductive adhesive. The conductive adhesive may include or consist essentially of a substantially isotropic conductive adhesive electrically connecting the first contact only to the first trace and the second contact only to the second trace. A non-conductive adhesive material may be disposed in the gap. The conductive adhesive may be an anisotropic conductive adhesive (ACA) electrically connecting the first contact only to the first trace and the second contact only to the second trace. A portion of the ACA may be disposed in the gap and may substantially isolate the first contact from the second contact. The electrical coupling may include or consist essentially of wire bonding and/or soldering. The first and second conductive traces may include or consist essentially of silver, gold, aluminum, chromium, copper, and/or carbon. The substrate may include or consist essentially of polyethylene naphthalate, polyethylene terephthalate, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, and/or paper. The reflectivity of the substrate for a wavelength emitted by the light-emitting element and/or the cured phosphor may be greater than 80%. The transmittance of the substrate for a wavelength emitted by the light-emitting element and/or the cured phosphor may be greater than 80%. The light-emitting element may include or consist essentially of a semiconductor material including or consisting essentially of GaN, AlN, InN, and/or an alloy or mixture thereof. The light-emitting element may include or consist essentially of a light-emitting diode.
The cured phosphor may absorb at least a portion of light emitted from the light-emitting element and may emit converted light having a different wavelength, converted light and unconverted light emitted by the light-emitting element combining to form substantially white light. The substantially white light may have a color temperature in the range of 2000 K to 10,000 K. The cured phosphor may include or consist essentially of a plurality of discrete regions, at least one of which includes or consists essentially of the binder and phosphor particles. At least one of the regions may include or consist essentially of only the binder. A surface of the mold may include a plurality of raised portions whereby a plurality of indentations are formed in the cured phosphor. Disposing the at least a portion of the cured phosphor over the light-emitting element may include or consist essentially of at least partially inserting the light-emitting element into one of the depressions. The mold may include or consist essentially of a plurality of discrete regions for containing phosphor, such that the cured phosphor includes or consists essentially of a plurality of phosphor chips. After removing the cured phosphor from the mold, the cured phosphor may be separated (e.g., by laser cutting, knife cutting, die cutting, and/or sawing) into a plurality of discrete phosphor chips. One or more of the phosphor chips may each be disposed over an additional light-emitting element, and, for each additional light-emitting element, the phosphor chip may absorb at least a portion of light emitted from the additional light-emitting element and may emit converted light having a different wavelength, converted light and unconverted light emitted by the additional light-emitting element combining to form substantially white light. The substantially white light may have a color temperature in the range of 2000 K to 10,000 K. The substantially white light emitted collectively from the different light-emitting elements and phosphor chips may have a variation in color temperature of less than four, or even less than two, MacAdam ellipses. The thicknesses of the phosphor chips may vary by less than ±10%, or even by less than ±5%.
The light-emitting element may be electrically connected to circuitry for powering the light-emitting element and/or to circuitry for controlling an optical output characteristic (e.g., luminous flux, correlated color temperature, color point, and/or color rendering index) of the light-emitting element and cured phosphor. A surface of the mold may be stepped, whereby after curing the cured phosphor has a plurality of portions having different thicknesses. Disposing the phosphor within the mold may include controlling an amount of phosphor introduced into the mold in response to a feedback signal. The mold may include or consist essentially of glass, metal, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), plastic film, tape, adhesive on a plastic film, metal, acrylic, polycarbonate, a polymer, and/or polytetrafluoroethylene. An optical element (e.g., a lens) may be associated with the light-emitting element. The at least a portion of the cured phosphor may have a curved shape. The binder may include or consist essentially of silicone (e.g., PDMS) and/or epoxy). The light-conversion material may include or consist essentially of a plurality of phosphor particles.
These and other objects, along with advantages and features of the invention, will become more apparent through reference to the following description, the accompanying drawings, and the claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations. Reference throughout this specification to “one example,” “an example,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present technology. Thus, the occurrences of the phrases “in one example,” “in an example,” “one embodiment,” or “an embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, routines, steps, or characteristics may be combined in any suitable manner in one or more examples of the technology. The term “light” broadly connotes any wavelength or wavelength band in the electromagnetic spectrum, including, without limitation, visible light, ultraviolet radiation, and infrared radiation. Similarly, photometric terms such as “illuminance,” “luminous flux,” and “luminous intensity” extend to and include their radiometric equivalents, such as “irradiance,” “radiant flux,” and “radiant intensity.” As used herein, the terms “substantially,” “approximately,” and “about” mean ±10%, and in some embodiments, ±5%. The term “consists essentially of” means excluding other materials that contribute to function, unless otherwise defined herein. Nonetheless, such other materials may be present, collectively or individually, in trace amounts.
In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:
The next step in process 100 is to provide a phosphor. In one embodiment, the phosphor includes or consists essentially of a phosphor and a binder. In some embodiments the phosphor and binder are mixed, for example in a centrifugal mixer, with or without a partial vacuum over the mixture.
In step 130 the phosphor is formed in the mold, as shown in
In some embodiments, a mold top or mold cover 231 (as shown in
In some embodiments of this example, one or more portions of mold 230 and/or mold top 231 have one or more openings or through-holes 233 that provide an overflow pathway for phosphor 310 during the mating process, as shown in
In step 140, phosphor 310 is cured. Curing may include or consist essentially of heating, exposure to radiation of various sources, for example visible, UV and/or IR light, or chemical curing (i.e., addition of an additional agent that promotes cross-linking in the binder). In one embodiment, phosphor 310 is cured by UV or other radiation and mold 230 is transparent to such radiation. In one embodiment, mold 230 is held within the curing equipment prior to or just after step 130 of
In step 150 the cured phosphor 310, now identified as phosphor 311, is removed from mold 230. At this point in the process, phosphor 311 is a solid having parallel or substantially parallel face 320 and face 330, where the thickness bounded by face 320 and face 330 is uniform or substantially uniform. In one embodiment, the thickness uniformity of phosphor 311 is within about ±15%, within about ±10%, within about ±5% or within about ±1%. In one embodiment, phosphor 311 has a thickness in the range of about 5 μm to about 500 μm; however, the thickness of phosphor 311 is not a limitation of the present invention, and in other embodiments phosphor 311 is thinner or thicker. In one embodiment, the compositional uniformity of phosphor 311, i.e., the distribution of phosphor powder in the binder, is uniform to within about ±15%, within about ±10%, within about ±5% or within about ±1%. In some embodiments, the area of phosphor 311 is in the range of about 0.25 mm2 to about 400 cm2; however, the area of phosphor 311 is not a limitation of the present invention, and in other embodiments the area of phosphor 311 is smaller or larger.
In some embodiments, phosphor 311 is separated into multiple pieces prior to use. Separation of phosphor 311 may be performed via any of multiple techniques, for example laser cutting, cutting with a knife, die cutting, saw cutting, or the like. In some embodiments, separation of phosphor 311 into multiple pieces is done before step 150 (removal of phosphor from mold) while in other embodiments separation of phosphor 311 into multiple pieces is done after step 150.
In some embodiments, phosphor 311 is transferred from mold 230 to a flexible and optionally adhesive film 510, as shown in
In some embodiments, mold 230 includes multiple depressions or wells into which phosphor 310 is formed, permitting formation of structures such as that shown in
The process detailed above generally produces uniform or substantially uniform phosphor pieces or chips 312. These may then be applied to LEEs, for example to achieve white light emission from the combination of the LEE and the phosphor chip; at least a portion of the light emitted by the LEE is absorbed by phosphor chip 312, and at least a portion of the absorbed light is re-emitted at a different wavelength. In one embodiment, white light is formed from a structure including or consisting essentially of a LEE emitting in the blue wavelength range (about 440 μm to about 470 μm), for example a blue LED and one or more phosphors emitting in the yellow-red range, such that the combination produces light that appears white to the eye. In one embodiment, the white light is visible light with a spectral power distribution whose chromaticity is close to the blackbody locus in the CIE 1931 xy or similar color space. In one embodiment, white light may have a correlated color temperature (CCT or color temperature) in the range of about 2000K to about 10,000K. Embodiments of the invention are not limited to materials, processes and structures that produce white light; in other embodiments these materials, structures and processes are used to produce any color light.
Application of phosphor chip 312 to the LEE may be performed in any of a variety of ways and with any of a number of attachment agents (such as clips, frames, or adhesion agents). In one embodiment phosphor chips 312 are picked from the structure shown in
In one embodiment phosphor chip 312 is applied to the LEE using an adhesion agent that is distinct from phosphor chip 312 and/or from the LEE. In one embodiment an adhesive or glue is disposed between the LEE and phosphor chip 312. In various embodiments this may be done using a liquid adhesive which may be sprayed, dispensed, screen printed, or stencil printed onto the LEE prior to application of phosphor chip 312. In one embodiment an adhesion agent may be applied to one side of phosphor chip 312 and that side applied to the LEE. Application of the adhesion agent to phosphor chip 312 may be done in ways similar to application of the adhesion agent to the LEE, as described herein. In other embodiments the adhesion agent may be applied to the cured phosphor before singulation into discrete chips.
In some embodiments the adhesion agent may include a curable adhesion agent, where the curing is activated by exposure to air, radiation, for example heat, UV radiation or the like, or moisture or by other means. In some embodiments the adhesion agent may have more than one component. For example in one embodiment a two-component adhesion agent may be utilized by application of a first part to phosphor chip 312 and a second part to the LEE, where the agent becomes adhesive when the two parts are brought in contact. In some embodiments such an approach may require additional activation for curing, while in others that is not required. Advantageously, a two-component system may be used in one embodiment by application of a first component to the phosphor before singulation into chips. In a similarly advantageous fashion, radiation or otherwise activated adhesives may be applied to the phosphor before singulation.
Adhesion agents preferably have high transparency to all or a significant portion of the wavelengths and/or radiant flux emitted by the LEE. In some embodiments the adhesion agent may be the same or similar material that is used as the binder or matrix for the phosphor chip.
In some embodiments of the present invention phosphor chip 312 may be held in place mechanically, for example by fitting into a frame or clip on the substrate surrounding the LEE, as shown in the examples in
In some embodiments of the present invention a transparent transfer tape may be applied to the phosphor before singulation into chips. In some embodiments a liner covers the side of the transfer tape opposite the phosphor. In some embodiments the phosphor and transfer tape are singulated in one step, while in other embodiments this is a multi-step process. Singulation may be accomplished in some embodiments using means described herein for phosphor singulation, for example laser cutting, knife cutting, shearing, rotary wheel cutting or the like. The method of singulation is not a limitation of the present invention. In embodiments where a liner is present, the liner is removed and the phosphor chip adhered to the LEE. Transfer tapes preferably have high transparency to all or a significant portion of the wavelengths and/or radiant flux emitted by the LEE.
In some embodiments high transparency means a transmissivity greater than 90% for all of the radiant flux incident on it from the LEE. In some embodiments high transparency means a transmissivity greater than 95% for all of the radiant flux incident on it from the LEE. In some embodiments high transparency means a transmissivity of greater than 90% for wavelengths in the range of about 420 nm to about 700 nm. In some embodiments high transparency means a transmissivity of greater than 95% for wavelengths in the range of about 420 nm to about 700 nm.
Advantageously, embodiments of the present invention produce phosphor chips 312 that have uniform or substantially uniform thickness and uniform or substantially uniform distribution of phosphor particles in the binder. The thickness and distribution, or loading, of the phosphor particles may have a strong impact on the uniformity of the color temperature of the light. In systems with multiple LEEs, and in particular arrays with tens to thousands of LEEs, it may be otherwise difficult to achieve a uniform phosphor coating over all of the LEEs, resulting in non-uniform color temperature.
Multiple-step MacAdam ellipses that encompass larger ranges of color around the center point may be constructed. The black body locus is in general aligned with the major axis of a MacAdam ellipse, meaning that the eye is less sensitive to color differences along the black body line, which equates to red/blue shifts, than to differences perpendicular to the black body line, which equates to a green/magenta shift. Furthermore, with respect to phosphor-converted white light sources, the variation in the minor axis direction 630 is in large measure determined by the LEE (typically a LED) wavelength variation, while the variation in the major axis direction 640 may be determined by the phosphor concentration and thickness. While there are many recommendations as to how tight the color temperature uniformity should be (as measured by MacAdam ellipses), it is clear that a variation encompassed within a smaller step number of MacAdam ellipses (smaller ellipse) is generally more uniform than one encompassed within a larger step number of MacAdam ellipses (larger ellipse). For example, a four-step MacAdam ellipse encompasses about a 300K color temperature variation along the black body locus, centered at 3200K, while a two-step MacAdam ellipse encompasses about a 150K color temperature variation along the black body locus, centered at 3200K.
The importance of uniform thickness and phosphor concentration in phosphor chips 312 may be observed in relation to the MacAdam ellipse on the chromaticity chart of
LEE substrate 720 may include or consist essentially of a semicrystalline or amorphous material, e.g., polyethylene naphthalate (PEN), polyethylene terephthalate (PET), acrylic, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, and/or paper. LEE substrate 720 may also include or consist essentially of a rigid or flexible circuit board, for example FR4, metal core printed circuit board (MCPCB), polyimide or the like. LEE substrate 720 may be substantially flexible, substantially rigid or substantially yielding. In some embodiments, the substrate is “flexible” in the sense of being pliant in response to a force and resilient, i.e., tending to elastically resume an original configuration upon removal of the force. A substrate may be “deformable” in the sense of conformally yielding to a force, but the deformation may or may not be permanent; that is, the substrate may not be resilient. Flexible materials used herein may or may not be deformable (i.e., they may elastically respond by, for example, bending without undergoing structural distortion), and deformable substrates may or may not be flexible (i.e., they may undergo permanent structural distortion in response to a force). The term “yielding” is herein used to connote a material that is flexible or deformable or both.
LEE substrate 720 may include multiple layers, e.g., a deformable layer over a rigid layer, for example, a semicrystalline or amorphous material, e.g., PEN, PET, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, paint, plastic film and/or paper formed over a rigid substrate for example including, acrylic, aluminum, steel and the like. Depending upon the desired application for which embodiments of the invention are utilized, LEE substrate 720 is substantially optically transparent, translucent, or opaque. For example, LEE substrate 720 may exhibit a transmittance or a reflectivity greater than about 80% for optical wavelengths ranging between approximately 400 nm and approximately 700 nm. In some embodiments, LEE substrate 720 exhibits a transmittance or a reflectivity of greater than about 80% for one or more wavelengths emitted by LEE 710 and/or phosphor chip 312. LEE substrate 720 may also be substantially insulating, and may have an electrical resistivity greater than approximately 100 ohm-cm, greater than approximately 1×106 ohm-cm, or even greater than approximately 1×1010 ohm-cm.
Conductive traces 730 may include or consist essentially of any conductive material, for example metals such as gold, silver, aluminum, copper and the like, conductive oxides, carbon, etc. Conductive traces 730 may be formed on LEE substrate 720 by a variety of means, for example physical deposition, plating, lamination, lamination and patterning, electroplating, printing or the like. In one embodiment, conductive traces 730 are formed using printing, for example screen printing, stencil printing, flexo, gravure, ink jet, or the like. Conductive traces 730 may include or consist essentially of a transparent conductor, for example, a transparent conductive oxide such as indium tin oxide (ITO). Conductive traces 730 may include or consist essentially of one or more materials. Conductive traces 730 may optionally feature stud bumps to aid in electrical coupling of conductive traces 730 to LEEs 710. Conductive traces 730 may have a thickness in the range of about 0.05 μm to about 250 μm. While the thickness of one or more of the conductive traces 730 may vary, the thickness is generally substantially uniform along the length of the conductive trace 730 to simplify processing. However, this is not a limitation of the present invention and in other embodiments the conductive trace thickness or material varies.
In one embodiment, one or more LEEs 710 are electrically coupled to conductive traces 730 using conductive adhesive, e.g., an isotropically conductive adhesive and/or an anisotropically conductive adhesive (ACA), as described in U.S. patent application Ser. No. 13/171,973, filed Jun. 29, 2011, the entire disclosure of which is incorporated by reference herein. An ACA is a material that permits electrical conduction only in the vertical direction but insulates the conductive trace 730 from each other. As used here, ACA may be provided in any form, for example paste, gel, liquid, film, or otherwise. ACAs may be utilized with or without stud bumps in accordance with embodiments of the present invention.
Various embodiments may utilize one or more other electrically conductive adhesives, e.g., isotropically conductive adhesives, in addition to or instead of one or more ACAs. Various embodiments may utilize wire bonding, thermosonic bonding, ultrasonic bonding, or solder as the method to connect LEEs 710 to conductive traces 730. The method of attachment and/or electrical coupling of LEE 710 to conductive traces 730 are not a limitation of the present invention.
A further advantage of the aforementioned approach is that it is has a relatively high efficiency of use of the phosphor, which may be relatively expensive. In large arrays of LEEs, the LEE pitch (distance between LEEs) may be on the order of about 3 mm to about 20 mm. In some embodiments, a large array has an area in the range of about 100 cm2 to about 3600 cm2 or to about 10,000 cm2 or larger. If the entire area were to be covered by phosphor, this would require a very large amount of phosphor, most of which would not be optically active. As an example, assume an array size of about 2500 cm2 and a pitch of about 5 mm; this results in an array of 100×100 LEEs, for a total of 10,000 LEEs. If each LEE is associated with a phosphor chip having a size of about 1.5 mm×about 1.5 mm, this results in a phosphor area for the present invention of about 225 cm2 (excluding kerf loss). This is about a 10× reduction in the area of phosphor required for such an array. As the LEE pitch increases, the area reduction increases.
The structure shown in
In the embodiment shown in
In the embodiment shown in
In some embodiments, LEEs 710 and/or 910 may be formed in an indentation or well 1010 such that all or a portion of an LEE 710 and/or LEE 910 is within well 1010, as shown in
In the examples above, the phosphor chip 312 is generally shown as a uniform rectangular solid having substantially smooth surfaces; however, this is not a limitation of the present invention, and in other embodiments phosphor chip 312 is shaped in any manner and/or may have roughened, patterned or textured surfaces, with such surface features in a regular, periodic or random pattern. In some embodiments, shaping and/or patterning or texturing of the surface is achieved during the formation or molding process, while in other embodiments shaping and/or patterning or texturing are performed after the phosphor is molded or after it is cured or partially cured.
In another embodiment, one or more surfaces of phosphor chip 311 are non-smooth, for example roughed, textured or patterned. In one embodiment, the non-smooth surface reduces total internal reflection (TIR) within phosphor chip 311 and achieves improved light extraction. In another embodiment, phosphor chip 311 is shaped in a lens shape. Such a lens may be a hemisphere, a paraboloid, a Fresnel optic or any other shape. In one embodiment, such a lens may be used to achieve a specific and desired light-distribution pattern. In one embodiment, phosphor chip 311 includes a photonic crystal formed on all or a part of the surface of phosphor chip 311, for example on all or a portion of the top surface of phosphor chip 311. In one embodiment, the photonic crystal increases the intensity of light exiting phosphor chip 311 in a particular direction.
In one embodiment, mold 230 features raised regions or bumps 1110 having substantially the size of LEE 710 or larger, as shown in
In another embodiment, phosphor 310 and 311 and phosphor chip 312 include or consists essentially of multiple discrete layers. In one embodiment, a first layer 1420 includes or consists essentially of a transparent material such as binder or matrix material 740 and a second layer 1410 includes or consists essentially of a phosphor layer or phosphor-containing layer, as shown in
In the above discussion, mold surface 200 (
In one embodiment, the thickness of phosphor 310, and thus the thickness of phosphor chip 312, is controlled by feedback during the filling process of mold 230. In one embodiment, phosphor 310 is excited by an appropriate pump source, for example a LEE such as a LED or laser, and the resulting white-light color temperature measured. When the target white-light color temperature is reached, the fill mechanism is notified to stop the filling of mold 230.
The approach described above provides various apparatus and methods to make uniform phosphor chips 312, resulting in highly uniform optical characteristics of phosphor chips 312 and LEEs 710. However, the uniformity of the optical characteristics may also depend on the optical characteristics of the LEE 710, in particular its emission wavelength. Referring back to
In another embodiment, a first layer of phosphor 310 is formed and is cured, uncured or partially cured, and then a second layer of phosphor 310 is formed over one or more portions of the initial phosphor that was formed, in response to a need for varying thickness phosphor chips 312. A schematic of such a structure is shown in
In another embodiment, a set of dividing grids is formed in mold 230 prior to formation of phosphor 310. The grids divide phosphor 310 into smaller regions, which after curing form phosphor chips 312. This is an alternate approach to cutting or separation of the phosphor after curing.
The arrangement of phosphor chips 312 makes them amenable to transfer or pick-and-place operations of multiple units at a time. The techniques described here permit the formation of relatively large rectangular or square arrays, from which a multiple tool pick-and-place or stamp operation may be fed with almost 100% utilization of all phosphor chips 312 in the array, where the pick or stamp pitch is, in some embodiments, an integer multiple of the pitch of phosphor chips 312 in the source array.
In some embodiments, the approaches described above to make multiple phosphor chips 312 are combined with testing and sorting to produce bins or groups of phosphor chips 312 having relatively narrowly distributed characteristics. For phosphor chips such properties may be determined alone or in combination with one or more LEEs 710. Such characteristics may include electrical characteristics such as forward voltage, leakage current, etc., and/or optical characteristics such as color temperature, color rendering index, efficiency, light output power and the like.
The approaches described above may permit batch or bulk fabrication of relatively large numbers of phosphor chips 312 in an economical manner with relatively tight distributions of characteristics. In particular, these approaches lead to the manufacture of cost-effective phosphor chips 312, that when combined with LEEs 710, have relatively narrow color temperature variations. In some embodiments, these approaches lead to a plurality of combinations of phosphor chips 312 and LEE 710 having a color temperature range of less than about five MacAdam ellipses, or less than three MacAdam ellipses, or less than two MacAdam ellipses or even less than one MacAdam ellipse.
The methods described above may permit the manufacture of very large arrays of phosphor chips 312 in an economical manner with a relatively narrow distribution in optical and mechanical characteristics. In some embodiments, the phosphor chip 312 has a side dimension of about 250 μm to about 5 mm and the kerf is about 10 μm to about 50 μm. In one embodiment, phosphor chips 312 have a pitch of about 1000 μm. This leads to a density of phosphor chips of about 1.0/mm2 or about 100 phosphor chips 312 per square cm. The manufacturing approaches described above may be practiced on any arbitrary size area. In one embodiment the area is about 10 cm×about 10 cm, or about 1000 cm2. In this example, this leads to the ability to manufacture 100,000 phosphor chips 312 simultaneously. This is just one example and not meant to be limiting to the invention. In general the density of phosphor chips 312 may vary with the size of LEEs 710 to which they are associated, the kerf, and the amount of phosphor desired on the sides of LEEs 710.
The above-described equipment, structures and methods may permit an integrated approach to the manufacture of phosphor chips 312 in a batch process at relatively low cost. This approach may include testing and sorting and binning, as is done with conventional packaged white LEDs. Trimming may be employed to further narrow the distribution of phosphor chip characteristics. In contrast to conventional packaged white LEDs, this approach may produce phosphor chips 312 that are then combined with LEEs 710. This reduces the cost and complexity of using white LEDs. A further advantage of embodiments of the invention is the use of a relatively larger portion of the manufacturing output of LEEs 710, because it provides an economical and straightforward way to match the phosphor characteristics to those of LEEs 710, in order to produce useful distributions of white light emitters.
In the structures described above, one or more surfaces of the phosphor, for example phosphor 311 or phosphor chips 312, may be patterned or roughened to improve light extraction from the phosphor, for example by reducing TIR in the phosphor. Such patterns or roughened or textured surfaces may be formed in a variety of ways. In one embodiment, these are formed by molding. In one embodiment, these are formed by techniques such as, for example laser ablation, wet or dry chemical etching, grinding, drilling or the like. In one embodiment, these may be formed by selective curing of the phosphor 310. In one embodiment, these features may be an array, such as a regular periodic array like a photonic crystal to aid in controlling the direction of the light exiting the phosphor. In some embodiments, such texturing, patterning or the like is present only on one surface, on one portion of one surface, or on multiple surfaces of the phosphor.
The systems described above may be combined with additional electronics to form an electronic device 1900 as shown in
As shown in
In some embodiments, the lighting systems described above further feature one or more optical elements. In some embodiments, one optical element is associated with each LEE 710, while in other embodiments multiple LEEs 710 are associated with one optical element, or multiple optical elements are associated with a single LEE 710, or no engineered optical element is associated with any LEE 710, and the LEE (and/or phosphor associated therewith) has only a flat or roughened surface. In one embodiment, the optical elements include features to scatter, diffuse and/or spread out light generated by the LEE 710 and/or phosphor 312. The optical elements may be formed by etching, polishing, grinding, machining, molding, embossing, extruding, casting, or the like. The method of formation of the optical elements is not a limitation of embodiments of the present invention.
Optic 2010 may be substantially optically transparent or translucent. For example, optic 2010 may exhibit a transmittance greater than 80% for optical wavelengths ranging between approximately 400 nm and approximately 600 nm. In one embodiment, optic 2010 includes or consists essentially of a material that is transparent to a wavelength of light emitted by LEE 710 and/or phosphor chip 312. Optic 2010 may be substantially flexible or rigid. In some embodiments, optic 2010 includes multiple materials and/or layers. Optical elements 2020 may be formed in or on optic 2010. Optic 2010 may include or consist essentially of, for example, acrylic, polycarbonate, polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, glass or the like. Optical elements 2020 may be formed by etching, polishing, grinding, machining, molding, embossing, extruding, casting, or the like. The method of formation of optical elements 2020 is not a limitation of the present invention.
Optical elements 2020 associated with optic 2010 may all be the same or may be different from each other. Optical elements 2020 may include or consist essentially of, e.g., a refractive optic, a diffractive optic, a TIR optic, a Fresnel optic, or the like, or combinations of different types of optical elements. Optical elements 2020 may be shaped or engineered to achieve a specific light distribution pattern from the array of light emitters, phosphors and optical elements.
As used herein, “alignment” and “aligned” may mean that the center of one structure, for example LEE 710, is aligned with the center of another structure, for example optical element 2010; however, this is not a limitation of the present invention and in other embodiments alignment refers to a specified relationship between the geometries of multiple structures.
The space between the back side of optic 2010 and phosphor chip 312, conductive traces 730 and LEE substrate 720, designated as region 2030 in
In
In
The examples discussed above show one LEE 710 associated with each phosphor chip 312. However, this is not a limitation of the present invention and in other embodiments a phosphor chip 312 is associated with multiple LEEs 710. Examples discussed above for phosphor chip 312 show phosphor chip 312 as being square and having sidewalls perpendicular to the sidewalls. However, this is not a limitation of the present invention, and in other embodiments phosphor chip 312 is rectangular, hexagonal, circular, triangular, or any arbitrary shape, and/or has sidewalls forming any angle with respect to the surface of phosphor chip 312.
While the phosphor chip has been used as part of a structure producing white light, this is not a limitation of the present invention, and in other embodiments, different color LEEs 710 and different phosphors (one or more) may be used to produce other colors, for example amber, green, or any arbitrary color or spectral power distribution. In some embodiments, the multiple LEEs 710 are all the same, while in other embodiments the multiple LEEs 710 include two or more groups of different LEEs 710, e.g., each emitting at different wavelengths.
Other embodiments of this invention have additional or fewer steps or components or may be modified or carried out in a different order. In general in the above discussion the arrays of light emitters, wells, optics and the like have been shown as square or rectangular arrays; however, this is not a limitation of the present invention and in other embodiments these elements are formed in other types of arrays, for example hexagonal, triangular or any arbitrary array. In some embodiments, these elements are grouped into different types of arrays on a single substrate.
The terms and expressions employed herein are used as terms and expressions of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof. In addition, having described certain embodiments of the invention, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of the invention. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive.
Claims
1. An electronic device comprising:
- a substrate having a plurality of conductive traces on a surface thereof, each pair of conductive traces being separated on the substrate by a gap therebetween;
- a plurality of light-emitting diode (LED) dies each spanning a gap between conductive traces and having first and second spaced-apart contacts each electrically coupled to one of the conductive traces defining the gap; and
- a plurality of discrete phosphor chips, each phosphor chip (i) disposed over an LED die and positioned to receive light therefrom, and (ii) attached to the LED die by an attachment agent discrete from the LED die and the phosphor chip,
- wherein each phosphor chip comprises (i) a light-conversion material and (ii) a binder comprising at least one of silicone or epoxy.
2. The electronic device of claim 1, wherein the attachment agent comprises at least one of a clip or a frame attached to the substrate.
3. The electronic device of claim 1, wherein the attachment agent comprises an adhesion agent adhering the phosphor chip to the LED die.
4. The electronic device of claim 3, wherein a transmittance of the attachment agent for a wavelength emitted by the LED die is greater than 90%.
5. The electronic device of claim 3, wherein a transmittance of the attachment agent for a wavelength emitted by the LED die is greater than 95%.
6. The electronic device of claim 3, wherein the adhesion agent comprises a transfer tape.
7. The electronic device of claim 1, wherein (i) each phosphor chip has a thickness, and (ii) a variation in the thicknesses of the phosphor chips is less than ±5%.
8. The electronic device of claim 1, wherein each phosphor chip absorbs at least a portion of light emitted from the LED die over which it is disposed and emits converted light having a different wavelength, converted light and unconverted light emitted by the LED die combining to form substantially white light.
9. The electronic device of claim 8, wherein the substantially white light emitted collectively from the different LED dies and phosphor chips has a color temperature variation less than four MacAdam ellipses.
10. The electronic device of claim 8, wherein the substantially white light emitted collectively from the different LED dies and phosphor chips has a color temperature variation less than two MacAdam ellipses.
11. The electronic device of claim 1, further comprising circuitry for powering at least one LED die.
12. The electronic device of claim 1, further comprising circuitry for controlling optical output characteristics of at least one LED die and the phosphor chip disposed thereover.
13. The electronic device of claim 12, wherein the optical output characteristic comprises at least one of chromaticity, luminous flux, correlated color temperature, color point, or color rendering index.
14. The electronic device of claim 1, further comprising an optical element associated with at least one LED die.
15. The electronic device of claim 1, wherein the first and second contacts are electrically coupled to conductive traces with a conductive adhesive.
16. The electronic device of claim 15, wherein the conductive adhesive comprises an anisotropic conductive adhesive (ACA).
17. The electronic device of claim 16, wherein (i) the ACA is disposed between the LED die and the substrate, and (ii) the ACA electrically connects a first conductive trace only to the first contact and a second conductive trace, different from the first conductive trace, only to the second contact.
18. The electronic device of claim 16, wherein a portion of the ACA is disposed in the gap and substantially electrically isolates the first contact from the second contact.
19. The electronic device of claim 1, wherein the first and second contacts are electrically coupled to conductive traces with at least one of wire bonds or solder.
20. The electronic device of claim 1, wherein each LED die comprises a bare LED die.
21. The electronic device of claim 1, wherein the light-conversion material comprises a plurality of phosphor particles.
22. The electronic device of claim 1, wherein a surface of the phosphor chip is textured.
23. The electronic device of claim 1, wherein the phosphor chip defines an indentation into which the LED die is at least partially disposed.
24. The electronic device of claim 1, wherein the conductive traces comprise at least one of silver, gold, aluminum, chromium, copper, or carbon.
25. The electronic device of claim 1, wherein the substrate comprises at least one of polyethylene naphthalate, polyethylene terephthalate, polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, or paper.
26. The electronic device of claim 1, wherein a reflectivity of the substrate for a wavelength emitted by at least one of the LED die or the phosphor chip is greater than 80%.
27. The electronic device of claim 1, wherein a transmittance of the substrate for a wavelength emitted by at least one of the LED die or the phosphor chip is greater than 80%.
28. The electronic device of claim 1, wherein the LED die comprises a semiconductor material comprising at least one of GaN, AlN, InN, or an alloy or mixture thereof.
29.-128. (canceled)
Type: Application
Filed: Jan 22, 2013
Publication Date: Jul 25, 2013
Inventor: Michael A. Tischler (Scottsdale, AZ)
Application Number: 13/746,574
International Classification: H05B 33/12 (20060101);
