Patent Application
20130056749
In various embodiments, the present invention generally relates to electronic devices, and more specifically to array-based electronic devices.
Light 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 LEDs and associated heat-sinking and thermal-management systems have limited the widespread utilization of LEDs, 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. In order to reduce costs, LED manufacturers have developed high-power LEDs that emit relatively higher light intensities by operating at higher currents. While reducing the package count, these LEDs require higher-cost packages to accommodate the higher current levels and to manage the significantly higher resulting heat levels. The higher heat loads and currents, in turn, typically require more expensive thermal-management and heat-sinking systems —for example, thermal slugs in the package, ceramic or metal submounts, large metal or ceramic heat sinks, metal core printed circuit boards and the like—which also add to the cost (as well as to the size) of the system. Higher operating temperatures may also lead to shorter lifetimes and reduced reliability. Finally, LED efficacy typically decreases with increasing drive current, so operation of LEDs at higher currents generally results in a reduction in efficacy when compared to lower-current operation.
A further problem associated with using a relatively small number of high-power LEDs in broad-area lighting, for example to replace fluorescent lighting systems, is that the light must be expanded from the relatively small area of the die (on the order of 1 mm2) to emit over a relatively large area (on the order of 1 ft2 or larger). Such expansion often results in decreased efficiency, reduced performance, and increased cost. For example, one possible approach is the use of an edge-lit panel that incorporates features in the panel that redirect or scatter light. However, such edge-lit structures typically have a relatively lower efficiency. In addition, it is difficult to achieve uniform light intensity over the entire emitting area, with the intensity generally being higher at the edge(s) near the light sources. Another problem is that the emission pattern from such devices is typically Lambertian, resulting in poor utilization of light and relatively high glare.
An alternate approach to producing broad-area lighting is to use a large array of small LEDs positioned over the desired emitting area. This minimizes or eliminates the cost and efficiency losses associated with optics required to spread out light from a small number of high-power LEDs. However, this approach typically involves a relatively complex fabrication process that in some cases may require highly customized chips, factors resulting in potentially reduced yields and higher costs. For example, this approach may involve (i) non-standard dies having a “dipole” geometry and a self-assembled alignment process that may be difficult to achieve with very high yield, or (ii) use of LED dies with top and bottom contacts (i.e., not the standard form of GaN-based LEDs used for general illumination). Top and bottom contacted GaN-based LEDs may be fabricated, but the increased processing cost, in part related to removal of the sapphire substrate, has traditionally only been justified for expensive large-area high-power LEDs. Finally, arrays of LEDs by themselves may produce an undesirable substantially Lambertian light distribution pattern.
A further problem with any LED-based system for general illumination is that integration with a light-conversion material (such as a phosphor) for the production of white light is often difficult, particularly in terms of uniformity and reproducibility. 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. A phosphor-coated LED generates white light by combining the short-wavelength radiant flux emitted by the semiconductor LED with long-wavelength radiant flux emitted by one or more phosphors. The 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.
As described in, e.g., Zhu, Y., N. Narendran, and Y. Gu. 2006. “Investigation of the Optical Properties of YAG:Ce Phosphor,” Sixth International Conference on Solid
State Lighting, Proc. SPIE Vol. 6337, 63370S-1 (“the Zhu reference”), the phosphor layer absorbs a portion of the incident short-wavelength radiant flux and re-emits long-wavelength radiant flux. In an exemplary YAG:Ce phosphor, as depicted by the graph in
The geometry of the phosphor relative to the LED generally has a very strong impact on the uniformity of the light characteristics. 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 the sides and top of the LED. To combat this problem, the LED may be placed in a reflecting cavity covered by a wavelength-converting material (e.g., a ceramic), such that all of the light from the LED exits the cavity through the converter. However, such 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.
Another issue with using phosphors to convert the short-wavelength radiant flux to long-wavelength radiant flux is isotropic emission from phosphors. Consequently, approximately half of the long-wavelength flux is emitted back towards the LED. As reported by the Zhu reference, 47% of the measured flux emitted by a YAG:Ce phosphor layer was directed back towards the blue light source, where a portion of it may be absorbed, resulting in reduced efficiency.
In order to be commercially viable, the manufacture of large arrays of LEDs desirably includes a cost-effective approach to position and form electrical connections to each LED in the array. Conventional wire bonding is too expensive when arrays number thousands of LEDs or more. As discussed above, a variety of self-assembly techniques for such arrays have been attempted, but these tend to be plagued by incomplete assembly, leading to inhomogeneous light distribution and low light output and efficiency.
Conductive adhesives are another approach that may be used to attach and electrically connect LEDs. However, as the LED die size shrinks, it becomes increasingly difficult to prevent short-circuiting of the die by the conductive adhesive. One recent advance facilitating the connectivity of LEDs to a variety of substrates is anisotropically conductive adhesive (ACA), which enables electrical interconnection in one direction (e.g., vertically between a device contact and a substrate contact), but prevents it in other directions (e.g., horizontally between contacts on a device or between contracts on a substrate). There are a number of different modes of operation of ACAs, including with and without pressure activation. As known in the art, a pressure-activated ACA typically includes an adhesive base, e.g., an adhesive or epoxy material, containing “particles” (e.g., spheres) of a conductive material or of an insulating material coated with a conductive material (such as metal) or a conductive material coated with an insulating material.
ACAs also have the advantage of applicability to relatively small contacts on an LED; in contrast, wire bonding typically requires a contact size on the order of 80 μm in diameter. The use of smaller contacts permits an increase in the emitting area relative to the total chip area, permitting a reduction in the overall chip size and a reduction in chip cost. Another advantage of using relatively smaller chips is that yield loss caused by “killer” particles or other defects (i.e., those whose presence in the area of the chip render it inoperative) is generally proportional to chip area, and thus smaller chips may have a higher yield and thus lower overall cost.
Referring again to
As discussed above, while arrays of LEDs may be used to produce uniform illumination across a large area, they do not, by themselves, necessarily produce a desired light-distribution pattern (e.g., one that provides desired illumination levels with low glare). One method to address this deficiency is to couple the array of light emitters with an array of optical elements designed to produce a specific light-distribution pattern. Such an array of optical elements may include arrays of refractive optical elements, Fresnel elements, or the like. These may be fabricated in a variety of optical materials such as acrylic or polycarbonate by, e.g., molding, casting, or embossing. Alignment of the optical elements with the LEDs may be critical in order to achieve the desired light-distribution pattern. This is particularly the case for an array of LEDs, where the overall light-distribution pattern is a superposition of the light emitted by each LED through each optical element and where different thermal budgets and/or thermal coefficients of expansion of different components of the system may generate misalignment during the fabrication process or in the field.
In view of the foregoing, a need exists for systems and procedures enabling the uniform and low cost integration of arrays of low cost light sources (such as LEDs), phosphors, and optical elements, as well as low cost, reliable LED-based lighting systems based on such systems and processes.
In accordance with certain embodiments, illumination devices (which are preferably planar) feature a plurality of light-emitting elements electrically connected in series, parallel, or in series/parallel fashion. The light-emitting elements may have light-conversion materials such as phosphors disposed over and/or around them, and may also be aligned to optical elements (e.g., lenses) disposed on or forming portions of an overlying optical substrate. In preferred embodiments, the integration of the light-conversion material and/or the optical elements with the light-emitting elements is repeatably and uniformly performed in parallel. For example, a substrate having the light-emitting elements disposed thereon (i.e., a “lightsheet”) may be directly bonded to the optical substrate, the light-emitting elements having been positioned for alignment with the optical elements of the optical substrate. Furthermore, low-cost methods such as screen printing may be utilized to form electrical conductors (e.g., “jumpers” or other electrical traces or connections) over the light-emitting elements or on the lightsheet to facilitate production of illumination devices incorporating arrays of tens, hundreds, or even thousands of light-emitting elements.
As utilized herein, an “optical substrate” is a material for receiving, manipulating, and/or transmitting light. An optical substrate may include or consist essentially of, e.g., a transparent or translucent sheet or plate, a waveguide and/or one or more (even an array of) optical elements such as lenses. For example, optical elements may include or consist essentially of refractive optics, reflective optics, Fresnel optics, total internal reflection optics, and the like. The optical substrate may include features or additional components or materials to scatter, reflect, or absorb light or a portion of light in the optical substrate, and it may confine light by total internal reflection prior to its emission from the optical substrate.
In an aspect, embodiments of the invention feature a method of forming an illumination system that includes or consists essentially of reversibly attaching a light-emitting element to a first substrate, mating (e.g., bonding) the first substrate to a second substrate to transfer the light-emitting element to the second substrate, removing the first substrate from the second substrate, and forming at least two conductors over the light-emitting element and the second substrate to thereby facilitate electrical connectivity to the light-emitting element.
Embodiments of the invention may feature one or more of the following in any of a variety of combinations. The light-emitting element may have at least two contacts disposed on a first side, and the first side of the light-emitting element may be reversibly attached to the first substrate. The first substrate may be mated to the second substrate with an adhesive material. The adhesive material may include or consist essentially of a releasable adhesive, and removing the first substrate from the second substrate may include or consist essentially of releasing the releasable adhesive (e.g., via exposure to heat and/or radiation). The second substrate may include a light-conversion material. The light-conversion material may be disposed on the second substrate, and the light-emitting element may be transferred to the second substrate on the light-conversion material. The second substrate may include a well therewithin. The light-conversion material may be disposed within and at least partially filling the well in the second substrate, and the light-emitting element may be disposed at least partially within the well after being transferred to the second substrate. The light-conversion material may include or consist essentially of a phosphor and a binder. The phosphor may include or consist essentially of lutetium aluminum garnet, yttrium aluminum garnet, a nitride-based phosphor, or a silicate-based phosphor. The binder may include or consist essentially of silicone, polydimethylsiloxane (PDMS), or epoxy. The light-conversion material may be cured. The conductors may be at least partially reflective to a wavelength of light emitted by the light-emitting element and/or a wavelength of light emitted by the light-conversion material. The second substrate may be substantially transparent to a wavelength of light emitted by the light-emitting element and/or a wavelength of light emitted by the light-conversion material. The light-conversion material may be disposed on a surface of the second substrate opposite the surface on which the light-emitting element is disposed, and the light-conversion material may be substantially aligned with the light-emitting element.
The light-emitting element may have two contacts disposed on a single side thereof. The contacts may be substantially coplanar with a surface of the second substrate after the light-emitting element is transferred thereto. Each of the two conductors may be formed over and in electrical contact with one of the contacts, and the conductors may be electrically isolated from each other after formation. A barrier may be formed between the contacts of the light-emitting element prior to formation of the conductors, and the barrier may prevent electrical contact between the conductors during formation thereof (e.g., by printing). The second substrate may include electrical traces thereon prior to being mated (e.g., bonded) to the first substrate, the light-emitting element may be transferred to the second substrate between two of the electrical traces, and each of the conductors may electrically connect a contact with an electrical trace. The light-emitting element may be electrically coupled to the electrical traces with a conductive adhesive (e.g., an anisotropic conductive adhesive). Each of the conductors may directly connect a contact of the light-emitting device to a contact of a different light-emitting element disposed on the second substrate.
The second substrate may include an optical element associated with the light-emitting element. The optical element may be disposed on a surface of the second substrate opposite the surface on the second substrate on which the light-emitting element is disposed. The second substrate may include a well aligned with the optical element.
The conductors may be formed by printing. The light-emitting element may include or consist essentially of a light-emitting diode. The light-emitting diode may include or consist essentially of one or more semiconductor materials selected from the group consisting of silicon, InAs, AlAs, GaAs, InP, AlP, GaP, InSb, GaSb, AlSb, GaN, AlN, InN, and mixtures and alloys thereof. The light-emitting element may have at least two contacts, and, prior to reversibly attaching the light-emitting element to the first substrate, the light-emitting element may be partially surrounded with a light-conversion material such that two contacts of the light-emitting element are not fully covered by light-conversion material.
In another aspect, embodiments of the invention feature a method of forming an illumination system. A light-conversion material is provided within each of a plurality of wells within an optical substrate comprising a plurality of optical elements. A lightsheet comprising a substrate, a plurality of electrical traces disposed on the substrate, and a plurality of light-emitting elements electrically coupled to the electrical traces is provided. The lightsheet is bonded to the optical substrate such that at least one light-emitting element is disposed within each well in the optical substrate.
Embodiments of the invention may feature one or more of the following in any of a variety of combinations. Providing the light-conversion material within the wells may include or consist essentially of dispersing the light-conversion material in liquid or gel form. Providing the light-conversion material within the wells may include or consist essentially of fitting a pre-shaped solid portion of the light-conversion material within each well. After bonding the lightsheet to the optical substrate, each well may be substantially filled by at least one light-emitting element and light-conversion material. During the bonding of the lightsheet and the optical substrate, a portion of the light-conversion material may flow from a well and adhere the lightsheet to the optical substrate. Each light-emitting element may be electrically coupled to the electrical traces with a conductive adhesive (e.g., an anisotropic conductive adhesive).
In yet another aspect, embodiments of the invention feature a method of forming an illumination system. Each of a plurality of bare-die light-emitting elements is partially surrounded with a light-conversion material such that two contacts of each light-emitting element are not fully covered by light-conversion material. Each of the light-emitting elements is inserted into a well in an optical substrate. Each well has an interior-surface shape complementary to the shape of the outer surface of the light-conversion material on the light-emitting element. Electrical traces are formed over each light-emitting element and the optical substrate to thereby facilitate electrical connectivity to the light-emitting elements.
Embodiments of the invention may feature one or more of the following in any of a variety of combinations. Each well in the optical substrate may be aligned with an optical element disposed on the optical substrate. The two contacts of each light-emitting element may be substantially coplanar with a surface of the optical substrate after the light-emitting elements have been inserted into wells. The electrical traces may be formed by printing. Each light-emitting element may be electrically coupled to the electrical traces with a conductive adhesive (e.g., an anisotropic conductive adhesive). A transparent material may be disposed between the interior surface of a well and the outer surface of the light-conversion material on the light-emitting element inserted into the ell. The transparent material may have an index of refraction of at least 1.35.
In a further aspect, embodiments of the invention feature a method of forming an illumination system. A plurality of light-emitting elements are attached to an optical substrate. Each light-emitting element is substantially aligned with an optical element on the optical substrate, electrically connected to at least two electrical traces on the optical substrate, and at least partially surrounded by a light-conversion material. A support substrate is bonded to the optical substrate such that each light-emitting element is disposed within a cavity in the support substrate. The inner surface of each cavity is reflective so as to direct light emitted by the light-emitting element therewithin toward the optical element substantially aligned with the light-emitting element.
Embodiments of the invention may feature one or more of the following in any of a variety of combinations. Each cavity may be substantially parabolic, and the light-emitting element disposed therewithin may be disposed at a focal point thereof. A discrete (i.e., separate) portion of the light-conversion material may be disposed over each light-emitting element after the light-emitting elements are attached to the optical substrate. The inner surface of each cavity may be reflective to a wavelength of light emitted by the light-conversion material. Each light-emitting element may be electrically coupled to the at least two electrical traces with a conductive adhesive (e.g., an anisotropic conductive adhesive).
In yet a further aspect, embodiments of the invention feature a light-emitting device including or consisting essentially of an optical substrate and a plurality of light-emitting elements. The optical substrate includes a plurality of cavities in a first surface thereof and a plurality of electrical traces disposed on the first surface thereof. Each light-emitting element is at least partially inserted into one of the cavities in the optical substrate, electrically connected to at least two electrical traces on the optical substrate, and at least partially surrounded by a light-conversion material. A plurality of optical elements may be disposed on a second surface of the optical substrate opposite the first surface. Each optical element may be substantially aligned with a cavity in the first surface.
In another aspect, embodiments of the invention feature a light-emitting device including or consisting essentially of an optical substrate, a plurality of electrical traces disposed on a first surface of the optical substrate, a plurality of light-emitting elements disposed over the first surface of the optical substrate, and a reflective surface disposed over each light-emitting element. Each light-emitting element is electrically connected to at least two electrical traces on the first surface of the optical substrate and at least partially surrounded by a light-conversion material. The light-conversion material may be disposed on the light-emitting element and/or on the reflective surface. The reflective surface may have a substantially parabolic shape, and the light-emitting element thereunder may be disposed at a focal point thereof. A plurality of optical elements may be disposed on a second surface of the optical substrate opposite the first surface. Each optical element may be substantially aligned with a light-emitting element.
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. As used herein, the term “substantially” means ±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:
Electronic device 300 may be formed in a roll-to-roll process, in which a sheet of the substrate material travels through different processing stations. Such roll-to-roll processing may, for example, include the formation of conductive traces 320, dispensing of the adhesive 360 (see
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 light-emitting elements include solid-state, organic, polymer, phosphor-coated or high-flux LEDs, laser diodes or other similar devices as would be readily understood. The emitted radiation of an LEE may be visible, such as red, blue or green, or invisible, such as infrared or ultraviolet. An LEE may produce radiation of a spread of wavelengths. An LEE may feature a phosphorescent or fluorescent material for converting a portion of its emissions from one set of wavelengths to another. An LEE may include multiple LEEs, each emitting essentially the same or different wavelengths. In some embodiments, an LEE is an LED that may feature a reflector over all or a portion of its surface upon which electrical contacts (e.g., contacts 312, 314) 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. Herein “reflective” is defined as having a reflectivity greater than 65% for a wavelength of light emitted by the LEE on which the contacts are disposed. In some embodiments, an LEE may include or consist essentially of a packaged LED, i.e., a bare LED die encased or partially encased in a package. In some embodiments, the packaged LED may also include a light-conversion material. In some embodiments, the light from the LEE may include or consist essentially of light emitted only by the light-conversion material, while in other embodiments, the light from the LEE may include or consist essentially of a combination of light emitted from the bare LED die and from the light-conversion material. In some embodiments, the light from the LEE may include or consist essentially of light emitted only by a bare LED die.
As shown in
As shown in
As discussed above, two or more semiconductor dies 310 may be connected to the same conductive traces 320 (i.e., within the same gap 370 between conductive traces 320), to provide enhanced functionality. The details of such electrical coupling are discussed in greater detail with reference to
Referring now to
Substrate 510 may include or consist essentially of one or more semiconductor materials, e.g., silicon, GaAs, InP, GaN, and may be doped or substantially undoped (e.g., not intentionally doped). In some embodiments substrate 510 includes or consists essentially of sapphire or silicon carbide, however the composition of substrate 510 is not a limitation of the present invention. Substrate 510 may be substantially transparent to a wavelength of light emitted by the semiconductor die 310. As shown for a light-emitting element, semiconductor layers 520 may include first and second doped layers 530, 540, which preferably are doped with opposite polarities (i.e., one n-type doped and the other p-type doped). One or more light-emitting layers 550, e.g., or one or more quantum wells, may be disposed between layers 530 and 540. Each of layers 530, 540, 550 may include or consist essentially of one or more semiconductor materials, e.g., silicon, InAs, AlAs, GaAs, InP, AlP, GaP, InSb, GaSb, AlSb, GaN, AlN, InN, and/or mixtures and alloys (e.g., ternary or quaternary, etc. alloys) thereof. In preferred embodiments, semiconductor die 310 is an inorganic, rather than a polymeric or organic, device. As referred to herein, semiconductor dies 310 may be packaged or unpackaged unless specifically indicated (e.g., a bare-die LED is an unpackaged semiconductor die). In some embodiments, substantially all or a portion of substrate 510 is removed prior to or after the bonding of semiconductor die 310 described below. Such removal may be performed by, e.g., chemical etching, laser lift-off, mechanical grinding and/or chemical-mechanical polishing or the like. In some embodiments all or a portion of substrate 510 is removed and a second substrate—e.g., one that is transparent to or reflective of a wavelength of light emitted by semiconductor die 310—is attached to substrate 510 or semiconductor layer 520 prior to or after the bonding of semiconductor die 310 as described below. In some embodiments substrate 510 includes or consists essentially of silicon and all or a portion of the silicon substrate 510 may be removed prior to or after the bonding of semiconductor die 310 described below. Such removal may be performed by, e.g., chemical etching, laser lift off, mechanical grinding and/or chemical-mechanical polishing or the like.
The structure shown in
In some embodiments, the semiconductor die 310 has a square shape, while in other embodiments semiconductor die 310 has a rectangular shape. In some preferred embodiments, to facilitate bonding (as described below) semiconductor die 310 has a shape with a dimension in one direction that exceeds a dimension in an orthogonal direction (e.g., a rectangular shape), and has an aspect ratio of the orthogonal directions (length to width, in the case of a rectangular shape) of semiconductor die 310 greater than about 1.2:1. In some embodiments, semiconductor die 310 has an aspect ratio greater than about 2:1 or greater than 3:1. The shape and aspect ratio are not critical to the present invention, however, and semiconductor die 310 may have any desired shape. In some embodiments, semiconductor die 310 has one lateral dimension less than 500 μm. Exemplary sizes of semiconductor die 310 may include about 250 μm by about 600 μm, about 250 μm by about 400 μm, about 250 μm by about 300 μm, or about 225 μm by about 175 μm. In some embodiments, semiconductor die 310 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, semiconductor die 300 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 μ2 or less than 10,000 μm2.
Because preferred embodiments facilitate electrical contact to contacts 570, 580 via use of a conductive adhesive rather than, e.g., wire bonds, contacts 570, 580 may have a relatively small geometric extent since adhesives may be utilized to contact even very small areas impossible to connect with wires or ball bonds (which typically require bond areas of at least 80 μm on a side). In various embodiments, the extent of one or both of contacts 570, 580 in one dimension (e.g., a diameter or side length) is less than approximately 100 μm, less than approximately 70 μm, less than approximately 35 μm, or even less than approximately 20 μm.
Particularly if semiconductor die 310 includes or consists essentially of a light-emitting device such as an LED or laser, contacts 570, 580 may be reflective (at least to some or all of the wavelengths emitted by semiconductor die 310) and hence reflect emitted light back toward substrate 510. In some embodiments, a reflective contact 580 covers a portion or substantially all of layer 540 and/or a reflective contact 570 covers a portion or substantially all of layer 530. In addition to reflective contacts, a reflector 590 (not shown in subsequent figures for clarity) may be disposed between or above portions of contacts 570, 580 and over portions or substantially all of layer 540 and 530. Reflector 590 is reflective to at least some or all wavelengths of light emitted by semiconductor die 310 and may include various materials. In one embodiment, reflector 590 is non-conductive so as not to electrically connect contacts 570, 580. Reflector 590 may be a Bragg reflector. Reflector 590 may include or consist essentially of one or more conductive materials, e.g., metals such as silver, gold, platinum, etc. Instead of or in addition to reflector 590, exposed surfaces of semiconductor die except for contacts 570, 580 may be coated with one or more layers of an insulating material, e.g., a nitride such as silicon nitride or an oxide such as silicon dioxide. In some embodiments, contacts 570, 580 feature a bond portion for connection to conductive traces 320 and a current-spreading portion for providing more uniform current through semiconductor die 310, and in some embodiments, one or more layers of an insulating material are formed over all or portions of semiconductor die 310 except for the bond portions of contacts 570, 580.
Referring again to
In preferred embodiments, the small size of semiconductor die 310, particularly of an unpackaged semiconductor die 310, and its abovementioned relatively low operating current and temperature, obviate the need for a relatively high thermal conductivity substrate as is conventionally used, for example a ceramic substrate (such as Al2O3, AlN or the like) or metal-core printed circuit board (MCPCB) or a discrete or integrated heat sink (i.e., a highly thermally conductive fixture (including, for example, metal or ceramic materials) such as a plate or block, which may have projections such as fins to conduct heat away and into the surrounding ambient) to be in thermal communication with semiconductor die 310. Rather, substrate 350 itself (as well as, e.g., the adhesive, the conductive traces, and even the surrounding ambient itself) provides adequate conduction of heat away from the semiconductor die 310 during operation.
Embodiments of the present invention involve lighting assemblies featuring light-emitting semiconductor dies attached to substrates using adhesives. Such assemblies may include an array of LEEs disposed over substrate 350. In some embodiments, the LEEs are disposed over substrate 350 in a two-dimensional array with a pitch in the range of about 3 mm to about 30 mm. For embodiments employing light-emitting semiconductor dies 310, the overall lighting assembly or module may produce at least 100 lumens, at least 1000 lumens, or even at least 3000 lumens, and/or may have a density of semiconductor die 300 greater than approximately 0.25 die/cm2 of area over which the semiconductor die 300 are disposed. Such light-emitting systems may feature semiconductor dies 300 having junction temperatures less than 110° C., 100° C., or even less than 90° C. Also, the heat density of such systems may be less than 0.01 W/cm2 of area over which the semiconductor die 300 are disposed. Furthermore, the heat density generated by systems in accordance with embodiments of the invention may be less than approximately 0.01 W/cm2, or even less than approximately 0.005 W/cm2, whereas conventional light-emitting devices typically have heat densities greater than approximately 0.3 W/cm2, or even greater than approximately 0.5 W/cm2.
In embodiments in which one or more of the semiconductor dies 310 is an LEE, a phosphor material may be incorporated to shift one or more wavelengths of at least a portion of the light emitted by the die 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). As used herein, “phosphor” refers to any material that shifts the wavelengths of light irradiating it and/or that is fluorescent and/or phosphorescent. A phosphor may also be referred to as a light-conversion material. Phosphors are typically available in the form of powders or particles, and in such case may be mixed in binders, e.g., silicone and/or epoxy. As used herein, a “phosphor” may refer to only the powder or particles or to the powder or particles with the binder. In some embodiments, optical elements are incorporated to permit engineering and control of the light distribution pattern.
Semiconductor dies 310 are disposed over conductive traces 320. Optical substrate 610 thus typically features an array of optical elements 620; in some embodiments, one optical element 620 is associated with each semiconductor die 310, while in other embodiments multiple semiconductor dies 310 are associated with one optical element 620, or multiple optical elements 620 are associated with a single semiconductor die 310. Also shown in
Conductive traces 320 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 320 may be formed on optical substrate 610 by a variety of means, for example evaporation, physical deposition, plating, lamination, lamination and patterning, electroplating, printing or the like. In some embodiments, conductive traces 320 may be formed by patterning a conductive layer formed over substrate 350, for example by removing a portion of the conductive layer by etching, e.g., wet chemical etching, dry etching, laser etching or the like. In one embodiment, conductive traces 320 are formed using printing, for example screen printing, stencil printing, flexo, gravure, ink jet, or the like. Conductive traces 320 may include or consist essentially of a transparent conductor, for example, a transparent conductive oxide such as indium tin oxide (ITO). Conductive traces 320 may include or consist essentially of a plurality of materials, for example a transparent conductive material in the region of the aperture of reflective surface 655 on optical element 620, and a relatively higher conductivity metallic conductive material outside of this region. This has the advantage of minimizing light loss when light exits the cavity, combined with maintaining a relatively low resistance of conductive trace 320, because the relatively higher resistivity transparent conductor is used only in the region where transparency is desired. Conductive traces 320 may optionally feature stud bumps positioned to align to contacts 312 and 314 of semiconductor dies 310. Conductive traces 320 may have a thickness in the range of about 0.01 μm to about 100 μm. While the thickness of one or more of the conductive traces 320 may vary, the thickness is generally substantially uniform along the length of the conductive trace 320 to simplify processing. However, this is not a limitation of the present invention, and in other embodiments the conductive trace may have a different thickness and/or the conductive trace thickness or material may vary.
Optical substrate 610 may be substantially optically transparent or translucent. For example, optical substrate 610 may exhibit a transmittance greater than 80% for optical wavelengths ranging between approximately 400 nm and approximately 600 nm. Optical substrate 610 may include or consist essentially of a material that is transparent to a wavelength of light emitted by semiconductor dies 310 and/or phosphor 625. Optical substrate 610 may be substantially flexible or rigid. Optical substrate 610 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. In some embodiments, optical substrate 610 includes multiple materials and/or layers. Optical elements 620 may be formed in or on optical substrate 610. For example, optical elements 620 may be formed by etching, polishing, grinding, machining, molding, embossing, extruding, casting, or the like. The method of formation of optical elements 620 is not a limitation of embodiments of the present invention. In some embodiments, all or portions of optical substrate 610 and/or optical elements 620 may include one or more layers reflective to a wavelength of light emitted by semiconductor dies 310 and/or phosphor 625.
Optical elements 620 associated with optical substrate 610 may all be the same or may be different from each other. Optical elements 620 may include or consist essentially of, e.g., a refractive optic, a diffractive optic, a total internal reflection (TIR) optic, a Fresnel optic, or the like, or combinations of different types of optical elements. Optical elements 620 may be shaped or engineered to achieve a specific light distribution pattern from the array of light emitters, phosphors and optical elements.
Reflective surface 655 may form a hemispherical or parabolic or other shape. In one embodiment, reflective surface 655 is formed by forming a reflective coating on the interior of a cavity 630 formed in a support substrate 640. Reflective coating 655 may include or consist essentially of a reflective material such as silver, gold, aluminum, copper, etc. In one embodiment, reflective coating 655 includes or consists essentially of a highly reflective white surface, for example, White97 manufactured by WhiteOptics LLC or MCPET manufactured by Furukawa. Reflective surface 655 may be formed by coating all or a portion of the surface of support substrate 640. In one embodiment, reflective surface 655 is formed by forming a depression in a yielding material that already has a reflective surface or coating. The support substrate 640 may include or consist essentially of a flat or substantially flat reflective surface facing semiconductor dies 310. In one embodiment a specular reflective surface 655 may form a parabolic shape and semiconductor dies 310 and/or phosphor 625 may be positioned substantially at the focal point of the parabolic shape, such that the light emitted out of the parabolic shape towards an optical element 620 is substantially collimated in a direction parallel to the axis of the parabolic shape. In some embodiments, the diameter of the aperture of the emitted light is less than about 0.25% of the diameter of optical element 620.
In one embodiment, phosphor 625 is formed over reflective surface 655 instead of around semiconductor dies 310. In one embodiment, a reflective material is formed over the phosphor 625, for example in sheet form, as shown in
The semiconductor dies 310 may be electrically coupled (or bonded) to conductive traces 320 (and optical substrate 610) using adhesive 360 as shown in
After or during the optional compression of semiconductor die 310 and optical substrate 610, adhesive 360 is cured by, e.g., application of energy, for example heat and/or ultraviolet light. For example, adhesive 360 may be cured by heating to a temperature ranging from approximately 80° C. to approximately 250° C., for a period of time ranging from approximately several seconds to 1 minute to approximately 30 minutes, depending on the properties of the adhesive.
In another embodiment, adhesive 360 includes or consists essentially of an isotropically conductive adhesive in the region between contacts 570, 580 and their respective conductive traces 320. In such embodiments, in the region between the conductive traces 320 and between contacts 570, 580, insulation may be maintained via absence of adhesive 360 or via the presence of a second, non-conductive adhesive, as shown in
Phosphor material 625 may be incorporated to shift the wavelengths of at least a portion of the light emitted by semiconductor dies 310 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 semiconductor dies 310). Exemplary procedures are herein described for integrating phosphors with the semiconductor dies 310 adhered to a substrate 710, as shown in
Referring to
Ce, Eu, etc., aluminates, nitrides, and the like. The specific components and/or formulation of the phosphor and/or matrix material are not limitations of the present invention.
The viscosity of the phosphor-infused matrix material may be varied by changing the matrix material and the amount of phosphor within the matrix material. In one embodiment a higher percentage of phosphor in the matrix results in a higher viscosity. The viscosity of the mixture may be adjusted to form the desired shape of phosphor 720 after dispense and curing. Curing may be performed using a variety of techniques, for example, thermal curing or UV curing. In one embodiment the phosphor may be partially cured prior to dispensing to increase its viscosity, in order to achieve a desired shape of phosphor 720. In one embodiment, the phosphor may be heated to a temperature below its cure temperature to reduce its viscosity.
As shown in
Some embodiments of structures such as those shown in
Multiple containment features 810 may be used to build up a plurality of layers of material over semiconductor dies 310. For example, as shown in
In another embodiment, containment features 810 include a coating over all or a portion of semiconductor die 310 to enhance the positioning of light-conversion material 720 over semiconductor die 310, or include a coating surrounding semiconductor dies 310 to aid in containment of light-conversion material 720 over semiconductor dies 310. Containment feature 810 may include a low-surface-tension coating, for example a fluorocarbon such as NyeBar manufactured by Nye Lubricants. In one embodiment, containment feature 810 includes a hydrophobic coating or a hydrophilic coating. In one embodiment containment feature 810 includes a perfluoro siloxane. Such coatings may be applied by brush, printing, for example printing, screen printing, flexo, gravure, ink jet or the like, dispensing, spraying or any other method. Containment feature 810 may include a coating to increase the contact angle of light-conversion material 720 on substrate 710. It is to be understood in this discussion that light-conversion material 720 may include a transparent material, a light-conversion material, or a material that provides scattering or diffusion of light emitted by semiconductor dies 310. In one embodiment light-conversion material 720 is formed by molding, for example compression molding.
In one embodiment, light-conversion material 720 is formed in small “caps” that are disposed over each semiconductor die 310.
Cap 1010 may be attached to optical substrate 610 (see
Cap 1010 may be formed using a variety of methods, for example injection molding, casting, machining, embossing or molding of a starting sheet or other techniques. In one embodiment, cap 1010 includes a support structure onto which light-conversion material 720 may be formed or deposited. Support substrate 640 (see
Optical elements 620 and wells 1410 may be formed simultaneously or sequentially. In one embodiment, optical elements 620 and/or wells 1410 are formed by removal of a portion of the material of optical substrate 610, for example by drilling, milling, sand blasting, etching or the like. Optical elements 620 and/or wells 1410 may be formed in or on optical substrate 610. For example optical elements 620 and/or wells 1410 may be formed by etching, polishing, grinding, machining, molding, embossing, casting drilling abrasive blasting or the like. The method of formation of optical elements 620 and/or wells 1410 is not a limitation of the present invention. Alignment of the geometry of wells 1410 and optical elements 620 may be achieved by a variety of methods known to those skilled in the art and without undue experimentation.
Optical elements 620 associated with optical substrate 610 may all be the same or may be different. Optical elements 620 may include for example a refractive optic, a diffractive optic, a total internal reflection (TIR) optic, a Fresnel optic or the like, or combinations of different types of optical elements. Optical elements 620 may be shaped or engineered to achieve a specific light distribution pattern from the array of light emitters, phosphors and optical elements.
Wells 1410 are shown as having a square or rectangular cross-section in
Wells 1410 may have any shape, as shown in top view in
A second component of structure 1300 shown in
Lightsheet substrate 1310 may include or consist essentially of a semicrystalline or amorphous material, e.g., polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, and/or paper. Lightsheet substrate 1310 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.
Lightsheet substrate 1310 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, 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, lightsheet substrate 1310 may be substantially optically transparent, translucent, or opaque. For example, lightsheet substrate 1310 may be reflecting or transmitting. In one embodiment lightsheet substrate 1310 exhibits a transmittance or a reflectivity greater than 80% for optical wavelengths ranging between approximately 400 nm and approximately 700 nm. In some embodiments lightsheet substrate 1310 exhibits a transmittance or a reflectivity of greater than 80% for one or more wavelengths emitted by semiconductor die 310 and/or light-conversion material 720. Lightsheet substrate 1310 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.
Optical substrate 610 with light-conversion material 720 may then be mated with lightsheet 1700, as shown in
In one embodiment, well 1410 is underfilled, filled, or overfilled with light-conversion material 720, such that after mating substantially all of well 1410 is filled with the combination of semiconductor dies 310 and light-conversion material 720, and an excess portion of light-conversion material 720 is forced from well 1410 to occupy a portion of the space between lightsheet 1700 and optical substrate 610. The excess portion of light-conversion material 720 that is forced from well 1410 to occupy a portion of the space between lightsheet 1700 and optical substrate 610 may act to hold lightsheet 1700 and optical substrate 610 together. In one embodiment, well 1410 has one or more void spaces that are not filled with either semiconductor dies 310 or light-conversion material 720.
The size of semiconductor dies 310 may be smaller than well 1410 and a modest amount of misalignment of the center of semiconductor dies 310 with the center of well 1410 may be acceptable. To aid in alignment, alignment features, for example alignment marks or pins or holes or other features on optical substrate 610 that mate or align to corresponding features on lightsheet 1700 may be used. Such alignment features may be formed on optical substrate 610 at the same time or a different time from the formation of wells 1410 and/or optical elements 620. Similarly, such alignment features on lightsheet 1700 may be formed at the same time or a different time as conductive traces 320.
In one embodiment, a reflective surface is formed on the back or front of lightsheet substrate 1310, so that any light emitted out the back side (i.e., the side adjacent to lightsheet substrate 1310) of semiconductor dies 310 is reflected back toward light-conversion material 720. Such a reflective coating may include a metal such as gold, silver, aluminum, copper or the like and may be deposited by evaporation, sputtering, chemical vapor deposition, plating, electroplating or the like. If the reflective coating is on the same side as conductive traces 320, the reflective coating may be electrically isolated from conductive traces 320 or may be removed in the regions occupied by conductive traces 320. The reflective coating may be formed either over or under conductive traces 320. The reflective coating may cover all or portions of lightsheet substrate 1310 and/or conductive traces 320. The reflective coating may also include other materials, e.g., a Bragg reflector, or one or more layers of a specular or diffuse reflective material. In one embodiment, lightsheet substrate 1310 is backed with a reflective material, for example any one as discussed above, or, e.g., White97 manufactured by WhiteOptics LLC or MCPET manufactured by Furukawa, or any other reflective material. In one embodiment lightsheet substrate 1310 includes or consists essentially of a material that is reflective to a wavelength of light emitted by semiconductor dies 310, for example white PET, white paper, MCPET, White97 or the like. In one embodiment, conductive traces 320 include a material reflective to a wavelength of light emitted by semiconductor dies 310 and/or light-conversion material 720 and are patterned to provide a region of reflective material surrounding semiconductor dies 310, as shown in
The lightsheet and optical substrate 610 may be mated in a variety of ways, as discussed above, or by other means. In one embodiment, mating is achieved by using an adhesive, a UV- or heat-cured adhesive, physical fasteners or the like. For example, an adhesive may be formed by spinning, spreading (for example using a Mayer bar or draw down bar), spraying, or may be in tape form, or may be deposited using a doctor blade technique, or by printing. The adhesive may cover substantially all of the mating surfaces or only one or more portions of the mating surfaces. In one embodiment the adhesive is transparent to a wavelength of light emitted by semiconductor dies 310 and/or light-conversion material 720. More than one material may be used to mate support the lightsheet and optical substrate 610. The adhesive over semiconductor dies 310 may have a low surface energy relative to the material in well 1410, and may thus be self-aligning, i.e., providing a driving force for a shift of the covered semiconductor dies 310 relative to the material in well 1410 causing these to align, for example by minimization of surface energy. In some embodiments, the lightsheet and optical substrate 610 are mated by means other than an adhesive, for example using mechanical fasteners, clamps, screws or the like, tape, or by other means. In one embodiment, material 720 shown in
It is important to note that alignment of optical elements 620 to well 1410 does not necessarily mean alignment of the center of optical elements 620 to the center of well 1410, but that their relative positions may be accurately and reproducibly controlled and manufactured. In other words, center-to-center alignment is not a limitation of this invention.
In one embodiment, the space between semiconductor dies 310 and cap 1010 is completely or partially filled with a matrix material or encapsulant that is transparent to a wavelength of light emitted by semiconductor dies 310. The encapsulant may aid in reducing TIR losses in semiconductor dies 310 and may also be used to adhere or help adhere optical substrate 610 to lightsheet substrate 1310. The light emitters of lightsheet 1700 may be partially or completely coated with a matrix material or encapsulant transparent to a wavelength of light emitted by semiconductor dies 310 prior to mating with optical substrate 610.
In yet another embodiment, the structure starts with that shown in
In one embodiment, optical substrate 610 has conductive traces 320 formed thereon prior to mating with temporary substrate 2210, as shown in the schematic top view in
Since the semiconductor dies 310 may be relatively small, for example on the order of about 300 μm by about 300 μm or smaller, and contacts 312, 314 on semiconductor dies 310 are even smaller, on the order of linear dimensions of about 80 μm or less, the ability to form and align small jumpers 2610 is an advantageous aspect of embodiments of the present invention. Jumper 2610 may have a length on the order of about 0.2 mm to about 5 mm and a width of about 20 μm to about 2 mm. The width in particular may have substantial variation if a trapezoidal shape, or a shape that has different widths at each end, is used, where the width is relatively small at the end coupling semiconductor dies 310 and relatively wide at the end coupling to conductive trace 320. Ink jet printing of conductive traces may achieve the required positional accuracies as well as resolution and is one implementation of this embodiment. However, ink jet printing is a serial process and thus may have relatively higher costs associated with relatively low throughput. In some embodiments it is desirable to have lower costs, which may be achieved through batch formation of jumpers 2610.
Jumpers 2610 may be printed, for example using a batch-type printing process such as screen printing, stencil printing, gravure or flexo printing. A relatively high level of resolution and/or accuracy may be required of these printing methods, particularly for relatively smaller light-emitting elements. For example, in one embodiment a semiconductor die 310 includes an LED with dimensions of about 200 μm by about 200 μm. If, for example, the electrical contacts extend in from opposite sides of the LED by about 50 μm, then the gap between contacts is about 100 μm. The jumper formation process may thus be capable of forming conductive traces with a gap less than about 100 μm in extent, for example less than about 75 or about 50 μm. Furthermore, the placement accuracy of the jumper is also on the order of about 75 μm or about 50 μm.
While many of the formation technologies, and in particular printing technologies, are capable of the resolution and accuracy discussed above, that resolution and accuracy come at a relatively higher cost, compared to the same processes but with lower resolution and accuracy. For example relatively higher resolution may be achieved in screen printing using high resolution screens and emulsions, for example synthetic fabric or metal screens. Such screens may require higher tension and additional equipment to mount the screens. Printing tools may be equipped with vision systems to achieve higher accuracy in alignment, for example alignment of jumper 2610 to the contacts of semiconductor die 310.
It may be desirable from a cost perspective to use relatively lower-resolution and/or less-accurate formation methods to, e.g., form jumper 2610 or other features. In one embodiment jumper 2610 is formed by a self-aligned method. This approach starts with a modification to the semiconductor die. A modified semiconductor die 2710 is shown in
During the printing process, barrier 2720 acts to prevent ink that will form jumpers 2610 from being deposited between contacts 312 and 314, as shown in
Alignment tolerances may be reduced by several approaches. First, as shown in
In another embodiment shown in
While semiconductor die 2710 and contacts 312 and 314 are shown as rectangular this is not a limitation of the present invention and in other embodiment they have other shapes, for example square, triangular, hexagonal or any other shape. In some embodiments the shape is determined to maximize the number of semiconductor dies that may be fabricated on a wafer while at the same time optimizing the aspect ratio of the semiconductor die and/or contact shape to provide robust manufacture.
The examples described above discuss forming jumpers 2610 between semiconductor die 310 or 2710 and conductive traces 320; however, in other embodiments jumpers 2610 and conductive traces 320 are formed in one step. In these embodiments the process is similar to that described above, however, conductive traces 320 are not formed at the point in manufacture shown in
In some embodiments, semiconductor dies 310 and/or 2710 have a thickness in the range of about 75 μm to about 150 μm. In some embodiments, the semiconductor dies are thinned to more easily permit jumpers 2610 or 3210 to provide coverage over the sidewall step of the semiconductor dies. In some embodiments semiconductor dies 310 or 2710 have sloped sidewalls to aid in providing coverage over the sidewall step of the semiconductor dies. In some embodiments semiconductor dies 310 or 2710 have a thickness in the range of about 2 μm to about 15 μm. In some embodiments semiconductor dies 310 or 2710 have a thickness about the same as the thickness of jumper 2610 or conductive trace 320 or 3210.
It should be noted that while optical substrates have been described above as including optical elements, in other embodiments an optical substrate does not include optical elements. For example,
The manufacture of system 3600 shown in
Temporary substrate 2210 may include any of a variety of materials, both rigid and flexible. For example temporary substrate 2210 may include metal, glass, plastic, ceramic or the like. In one embodiment temporary substrate 2210 includes or consists essentially of a semicrystalline or amorphous material, e.g., polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polycarbonate, polyethersulfone, polyester, polyimide, polyethylene, and/or paper. Temporary substrate 2210 may include multiple layers and/or be flexible.
Wells 3720 may then be filled or partially filled with light-conversion material 720 and temporary substrate 2210 removed, as shown in
Light-conversion material 720 may include a material transparent to a wavelength of light generated by light-emitting element 310 or may include a light-conversion material or both. A light-conversion material 720 may include a phosphor including or consisting essentially of, e.g., one or more silicates, nitrides, quantum dots, or other light-conversion materials, and may be suspended in an optically transparent binder (e.g., silicone or epoxy). Semiconductor dies 310 for use with one or more phosphors may emit substantially blue or ultraviolet light, and the use of the phosphor(s) may result in aggregate light that is substantially white, and which may have a correlated color temperature (CCT) ranging from approximately 2000 K to approximately 7000 K.
Examples of such dies are those including GaN, InN, AlN and various alloys of these binary compounds. Light-conversion material 720 may include a homogeneous or substantially homogeneous material or mixture, or a non-homogeneous material, or may include layers or other divisions of light-conversion and/or transparent materials. For example, in one embodiment a transparent material may first cover light-emitting element 310, and this may then be covered or partially covered by a light-conversion material.
In the next stage of manufacture semiconductor dies 310 may be electrically coupled together through conductive traces 3630, as shown in
In some embodiments the semiconductor dies and/or light-conversion materials are different within one lightsheet. For example, a lightsheet may include a plurality of semiconductor dies, each emitting at substantially the same wavelengths, but different composition, concentration or thickness light-conversion materials may be associated with different semiconductor dies. In one embodiment a yellow-emitting phosphor and a red-emitting phosphor may be formed in different groups of wells to provide improved color temperature and CRI and uniformity of color temperature and CRI. In one embodiment a lightsheet includes a plurality of semiconductor dies that may be divided into groups, and each group may emit light of a different wavelength. For example, in one embodiment a first group of semiconductor dies emits in the red wavelength range and a second group of semiconductor dies emits in the blue wavelength range. In one embodiment, a first group of semiconductor dies is optically coupled with a light-conversion material while a second group of semiconductor dies is not optically coupled with a light-conversion material.
In one embodiment a lightsheet includes a plurality of two or more different types of semiconductor dies, for example emitting at two or more different wavelengths. In one embodiment such a lightsheet includes the two or more different types of semiconductor die associated with or embedded in a single type of light-conversion material. In one version of this embodiment, the two or more different semiconductor dies are positioned near or next to each other and are associated with or embedded in the same portion of the light-conversion material.
In one embodiment a lightsheet includes two or more semiconductor dies associated with or embedded in two or more different types of light-conversion material. In one embodiment such a lightsheet includes the two or more semiconductor dies, where at least one of the two or more semiconductor dies is not associated with or embedded in a light-conversion material and the remaining two or more semiconductor dies are associated with or embedded in one or more types of light-conversion material.
In some embodiments semiconductor die 310′ may have a forward voltage that is different from that of semiconductor die 310 and in these cases it may be desirable to independently control the current in semiconductor dies 310 and 310′. For example, in the case of semiconductor die 310 including or consisting essentially of a GaN-based LEE emitting in the blue wavelength regime, the forward voltage may be in the range of about 2.5 V to about 3.5 V. In the case of semiconductor die 310′ including or consisting essentially of an InGaAlP-based LEE emitting in the red wavelength regime, the forward voltage may be in the range of about 1.8 V to about 2.8 V.
In one embodiment control element 4010 includes a second diode and in some examples the second diode may be the same as the semiconductor die it is in series with. Where control element 4010 includes a diode, in some embodiments the voltage drop across control element 4010 and semiconductor die 310′ may be selected to be the same or substantially the same as the voltage drop across the circuit elements in the other circuit leg (e.g., semiconductor die 310).
In yet another set of embodiments semiconductor die 310 and/or semiconductor die 310′ is associated with or covered or partially covered by light-conversion material 720 before attachment to a substrate, for example substrate 210 as shown in
White die 4100 may be used to produce embodiments of this invention, instead of forming light-conversion material 720 over semiconductor die 310 after attachment of semiconductor die 310 to a substrate. For example the structure of
In general in the above discussion the arrays of semiconductor dies, light emitting elements, 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 may be formed in other types of arrays, for example hexagonal, triangular or any arbitrary array. In some embodiments these elements may be grouped into different types of arrays on a single substrate.
In some embodiments, the LEEs of one or more lightsheets are of the same type. In some embodiments, the LEEs of one or more lightsheets may be different. In some embodiments, a single lightsheet may include multiple different types of LEEs. For example, different types of LEEs may include different sized LEEs or LEEs that have different electrical or optical characteristics, such as emission wavelength or spectral power density. In some embodiments, each string may include or consist essentially of multiple LEEs of the same type; however, this is not a limitation of the present invention and in other embodiments each string may include or consist essentially of more than one type of LEE, for example LEEs that emit light at different wavelengths or with different spectral power densities or have different sizes. In some embodiments, a lightsheet may feature multiple strings, where each string includes or consists essentially of multiple LEEs of the same type; however, this is not a limitation of the present invention and in other embodiments the lightsheet may include or consist essentially of multiple strings where each string may include or consist essentially of more than one type of LEE, for example LEE that emit light at different wavelengths or with different spectral power densities or have different sizes. The number of different types of LEEs is not a limitation of the present invention. In some embodiments, a lighting system includes or consists essentially of a plurality of lightsheets. The number of lightsheets and the number of different types of lightsheets within a lighting system is not a limitation of the present invention. In some embodiments, a lightsheet and/or lighting system may include a combination of bare-die LEEs and packaged LEEs.
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.
This application claims the benefit of and priority to U.S. Provisional Patent Application No. 61/531,676, filed Sep. 7, 2011, and U.S. Provisional Patent Application No. 61/589,908, filed Jan. 24, 2012, the entire disclosure of each of which is hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61531676 | Sep 2011 | US | |
| 61589908 | Jan 2012 | US |
