Patent Application
20070267642
One or more embodiments presented herein include a light-emitting device assembly which has been configured to effectively transfer thermal energy generated by a light-emitting device (e.g., an LED) to a supporting base (e.g., a core board) and ultimately to the surroundings, which may include an external heat sink. Such an assembly can include a light-emitting device, an optional package that can support the light-emitting device, and a base supporting the package. Alternatively, the package may be absent, and the base may directly support the light-emitting device (e.g., an LED die). The base may include a layer (e.g., a dielectric layer) on a substrate, wherein the substrate may be thermally conductive and/or electrically conductive. The layer may be a dielectric layer that can electrically isolate the substrate from other features (e.g., metal contacts) of the assembly. An aperture may be defined by the layer through which a thermally conductive material (e.g., a portion of the substrate) can extend to facilitate thermal communication between the substrate and the light-emitting device. The thermal communication with the light-emitting device can increase the removal of thermal energy generated by the light-emitting device.
Layer 106 can define an aperture 115, where the aperture 115 can enable a thermally conductive pathway to extend from the substrate 102 to the light-emitting die 118. The light-emitting die can be in direct or indirect thermal contact with the thermally conductive pathway that extends from the substrate, for example indirect thermal contact may result when the light-emitting die is supported by a package. The thermally conductive pathway between the light-emitting die 118 and the substrate 102 can have a minimum thermal conductivity of greater than about 25 W/m*K, greater than about 50 W/m*K, greater than about 100 W/m*K, or greater than about 200 W/m*K (e.g., about 400 W/m*K), thus increasing heat removal from the light-emitting device via substrate 102.
The thermally conductive pathway may include protrusion 110 that extends through the aperture, such that protrusion 110 may be disposed between the light-emitting die 118 and the substrate 102. Protrusion 110 may be any suitable localized feature that extends upwards from the substrate 102, and can have any suitable shape and dimensions, as the techniques described herein are not limited in this respect. In some embodiments, protrusion 110 is part of substrate 102 and protrudes upward through the aperture 115 in layer 106. In other embodiments, protrusion 110 may be formed of a thermally conductive material different than the material of the substrate 102 and may extend through the aperture 115 to contact the substrate 102 and form a part of the thermally conductive pathway. Protrusion 110 may be elevated with respect to layer 106, may be flush with layer 106, or may be recessed with respect to layer 106. When protrusion 110 is recessed with respect to layer 106, a thermally conductive filler material and/or attachment material (e.g., a solder) may be disposed on protrusion 110.
At least one electrical contact 104 may be supported by layer 106. Electrical contact(s) 104 can be a component of a circuit board assembly (not shown) that may also be disposed on layer 106. When electrical contact(s) 104 are included in the assembly, layer 106 may be an electrically insulating layer, such as a dielectric layer, which may electrically isolate the electrical contact(s) 104 from the substrate 102. In certain embodiments, the electrical contact(s) 104 and protrusion 110 are flush mount so as to be substantially level with each other and therefore facilitate attachment to package 108. Electrical contact(s) 104 may be connected to an external voltage source (not shown) that can provide power to the device.
Package 108 may have any suitable design and construction. In embodiments in which the package forms part of the thermally conductive pathway between the substrate 102 and light-emitting die 118, part or all of package 108 may be formed of a material having a sufficiently high thermal conductivity. In some cases, the package is formed of a thermally conductive ceramic such as aluminum nitride. The package may be electrically insulating, although it should be appreciated that the techniques presented herein are not limited in this respect. The package may include regions that are electrically insulating and regions that are electrically conductive, for example, vias filled with electrically conductive material (e.g., metal-filled vias, such as tungsten-filled vias) that allow electrical coupling between an exterior surface of the package and an interior surface of the package.
In some embodiments, the package includes a transparent layer 112 which functions as a window to emit light generated by light-emitting die 118. Package 108, as shown in
One or more light-emitting dies may be fixed to the package 108 with any suitable attachment material 116, including, but not limited to, solder (e.g., an alloy between two or more metals such as gold, germanium, tin, indium, lead, silver, molybdenum, palladium, antimony, zinc, etc.), metal-filled epoxy, thermally conductive adhesives, metallic tape, thermal grease, and/or carbon nanotube-based foams or thin films. Thermally conductive attachment materials typically have a suitably high thermal conductivity and therefore a low thermal resistance per unit contact area. Examples of suitable light-emitting dies that may be fixed to the package are described in further detail below.
Other components and features may be included in the light-emitting device assembly such as n-contact 124, p-contact 119, wire bonds 122, and electrical bond pads 120. N-contact 124 and p-contact 119 may be supported by package 108, while the electrical bond pad(s) 120 can be supported by the light-emitting die 118. Electrical bond pad 120 and n-contact 124 can be electrically coupled to each other through wire bonds 122. In the illustrative embodiment, n-contact 124 and p-contact 119 are respectively electrically connected to electrical contacts 104 by electrically conductive pathways 117 (e.g., formed of a metal, such as tungsten) that extend through vias that may be formed in the package.
Multiple electrical contact pads 120 can be supported on the surface of the light-emitting die. These contact bond pads are features on a device that can be electrically connected to a power source. Contact pads can be designed to improve current distribution in electronic devices such as LEDs. Suitable contact pad structures have been described in U.S. Patent Publication No. 2005-0051785, which is incorporated herein by reference in its entirety and is based on U.S. patent application Ser. No. 10/871,877, entitled “Electronic Device Contact Structures,” filed on Jun. 18, 2004.
Substrate 102 can be comprised of any material that has sufficiently high thermal conductivity. In some embodiments, substrate 102 comprises a metal, such as copper and/or aluminum. In another embodiment, substrate 102 may be a vapor plate, for example, a copper vapor plate, wherein the vapor plate can contain any type of fluid that facilitates the transfer of heat, such as air. Alternatively, or additionally, the substrate 102 may include at least one heat pipe, wherein the heat pipe may be filled or partially filled with a fluid to increase heat transfer and support at least one light-emitting die or light-emitting die package. Additionally, the heat pipe can be coupled to the substrate 102 to increase heat transfer from the light-emitting die via the substrate.
Base 150, which may include substrate 102 and protrusion 110, can facilitate the extraction of thermal energy that may be generated by the light-emitting die 118. Protrusion 110 and substrate 102 can also function as an electrical contact, and may be used in lieu of electrical contact member 104, as discussed below. In some embodiments, it may be preferable for protrusion 110 and substrate 102 to function as an electrical p-contact member, but this configuration is by no way limiting and the protrusion 110 and substrate 102 can also function as an electrical n-contact member.
It should be appreciated that although the aperture in layer 106 illustrated in
The supporting base structures described herein can be manufactured or fabricated using a variety of methods. Referring to
In an alternative embodiment, as illustrated in the schematics of
In an alternative embodiment, as shown in
In other embodiments, a protrusion comprising a thermally conductive material different than the material of the substrate may extend through the aperture to contact the substrate and form a part of the thermally conductive pathway. The thermally conductive material may be formed of any suitable material and in any suitable way. In one such embodiment, one or more diamond layers (e.g., synthetic diamond) may extend through the aperture to form part of the thermally conductive pathway. Diamond layers may be disposed, for example using a coating process, over one or more layers (e.g., metal layers, such as copper or aluminum layers) that may also extend through the aperture. Such processes can include chemical vapor deposition (CVD), physical vapor deposition (PVD), or any other suitable coating or deposition process known to those of ordinary skill in the art. In some embodiments, a thermally conductive coating may be formed on protrusion 110a, 110b, or 110c. In one such embodiment, protrusion 110a, 110b, or 110c may be coated with a diamond coating. Diamond coating layers may be disposed on other layers in any suitable manner, including but not limited to, using a synthetic diamond coating processes, as is known in the art. Other variations would be known to those of ordinary skill in the art.
Any number of modifications may be made to the light-emitting device assembly of
A backside of light-emitting die 118 may be electrically coupled to a p-contact 519. The light-emitting die 118 may be attached to the p-contact with an electrically conductive attachment material 516. The electrically conductive attachment material 516 may include solder (e.g., an alloy between two or more metals such as gold, germanium, tin, indium, lead, silver, molybdenum, palladium, antimony, zinc, etc.), electrical tape, or any other electrically conductive material. The p-contact 519 may be electrically coupled to the electrical via 517 of the package. Furthermore, the package can be attached to the base 150 by solder attach 114, which may also be electrically conductive. When part or all of protrusion 110 and part or all of substrate 102 are electrically conductive, for example when part or all of protrusion 110 and substrate 102 are formed of a metal (e.g., copper), an electrical contact to the light-emitting die 118 may be achieved by electrically contacting substrate 102.
Package 608 may include n-contact 624 and p-contact 625, and light-emitting die 618 may be flip-chip bonded to n-contact 624 and p-contact 625. N-electrical bond pad 620 may be bump-bonded to the n-contact 624 and the p-electrical bond pad 621 may be bump-bonded to p-contact 625. N-contact 624 and p-contact 625 may be electrically coupled to the exterior of the package 608 by any suitable contacting technique, as the techniques presented herein are not limited in this respect. In one embodiment, n-contact 624 and p-contact 625 may extend laterally (not shown) so as to electrically couple to respective electrical vias 117, such as metal-filled vias, for the n- and p-contacts. Alternatively, n-contact 624 and/or p-contact 625 may be contacted externally via wire bonds, for example through holes (not shown) in window 112 and/or the frame of package 608. Alternatively, package 608 may include electrical vias in the frame supporting the window 112 (not shown) and n-contact 624 and/or p-contact 625 may be wire-bonded to these electrical vias in the frame. In such contacting schemes, electrical vias 117 and electrical contacts 104 shown in
In some embodiments, protrusion 110 may be absent and mount 710 may be directly attached to the base by attachment material 114.
The active region of an LED can include one or more quantum wells surrounded by barrier layers. The quantum well structure may be defined by a semiconductor material layer (e.g., in a single quantum well), or more than one semiconductor material layers (e.g., in multiple quantum wells), with a smaller electronic band gap as compared to the barrier layers. Suitable semiconductor material layers for the quantum well structures can include InGaN, AlGaN, GaN and combinations of these layers (e.g., alternating InGaN/GaN layers, where a GaN layer serves as a barrier layer). In general, LEDs can include an active region comprising one or more semiconductors materials, including III-V semiconductors (e.g., GaAs, AlGaAs, AlGaP, GaP, GaAsP, InGaAs, InAs, InP, GaN, InGaN, InGaAlP, AlGaN, as well as combinations and alloys thereof), II-VI semiconductors (e.g., ZnSe, CdSe, ZnCdSe, ZnTe, ZnTeSe, ZnS, ZnSSe, as well as combinations and alloys thereof), and/or other semiconductors. Other light-emitting materials are possible such as quantum dots or organic light-emission layers.
The n-doped layer(s) 135 can include a silicon-doped GaN layer (e.g., having a thickness of about 4000 nm thick) and/or the p-doped layer(s) 133 include a magnesium-doped GaN layer (e.g., having a thickness of about 40 nm thick). The electrically conductive layer 132 may be a silver layer (e.g., having a thickness of about 100 nm), which may also serve as a reflective layer (e.g., that reflects upwards any downward propagating light generated by the active region 134). Furthermore, although not shown, other layers may also be included in the LED; for example, an AlGaN layer may be disposed between the active region 134 and the p-doped layer(s) 133. It should be understood that compositions other than those described herein may also be suitable for the layers of the LED.
As a result of openings 139, the LED can have a dielectric function that varies spatially according to a pattern which can influence the extraction efficiency and/or collimation of light emitted by the LED. In the illustrative LED 31, the pattern is formed of openings, but it should be appreciated that the variation of the dielectric function at an interface need not necessarily result from openings. Any suitable way of producing a variation in dielectric function according to a pattern may be used. For example, the pattern may be formed by varying the composition of layer 135 and/or emission surface 138. The pattern may be periodic (e.g., having a simple repeat cell, or having a complex repeat super-cell), periodic with de-tuning, or non-periodic. As referred to herein, a complex periodic pattern is a pattern that has more than one feature in each unit cell that repeats in a periodic fashion. Examples of complex periodic patterns include honeycomb patterns, honeycomb base patterns, (2×2) base patterns, ring patterns, and Archimedean patterns. In some embodiments, a complex periodic pattern can have certain openings with one diameter and other openings with a smaller diameter. As referred to herein, a non-periodic pattern is a pattern that has no translational symmetry over a unit cell that has a length that is at least 50 times the peak wavelength of light generated by active region 134. Examples of non-periodic patterns include aperiodic patterns, quasi-crystalline patterns, Robinson patterns, and Amman patterns.
In certain embodiments, an interface of a light-emitting device is patterned with openings which can form a photonic lattice. Suitable LEDs having a dielectric function that varies spatially (e.g., a photonic lattice) have been described in, for example, U.S. Pat. No. 6,831,302 B2, entitled “Light Emitting Devices with Improved Extraction Efficiency,” filed on Nov. 26, 2003, which is herein incorporated by reference in its entirety. A high extraction efficiency for an LED implies a high power of the emitted light and hence high brightness which may be desirable in various optical systems.
It should also be understood that other patterns are also possible, including a pattern that conforms to a transformation of a precursor pattern according to a mathematical function, including, but not limited to an angular displacement transformation. The pattern may also include a portion of a transformed pattern, including, but not limited to, a pattern that conforms to an angular displacement transformation. The pattern can also include regions having patterns that are related to each other by a rotation. A variety of such patterns are described in U.S. patent application Ser. No. 11/370,220, entitled “Patterned Devices and Related Methods,” filed on Mar. 7, 2006, which is herein incorporated by reference in its entirety.
Light may be generated by the LED as follows. The p-side contact layer can be held at a positive potential relative to the n-side contact pad, which causes electrical current to be injected into the LED. As the electrical current passes through the active region, electrons from n-doped layer(s) can combine in the active region with holes from p-doped layer(s), which can cause the active region to generate light. The active region can contain a multitude of point dipole radiation sources that generate light with a spectrum of wavelengths characteristic of the material from which the active region is formed. For InGaN/GaN quantum wells, the spectrum of wavelengths of light generated by the light-generating region can have a peak wavelength of about 445 nanometers (nm) and a full width at half maximum (FWHM) of about 30 nm, which is perceived by human eyes as blue light. The light emitted by the LED may be influenced by any patterned interface through which light passes, whereby the pattern can be arranged so as to influence light extraction and/or collimation.
In other embodiments, the active region can generate light having a peak wavelength corresponding to ultraviolet light (e.g., having a peak wavelength of about 370-390 nm), violet light (e.g., having a peak wavelength of about 390-430 nm), blue light (e.g., having a peak wavelength of about 430-480 nm), cyan light (e.g., having a peak wavelength of about 480-500 nm), green light (e.g., having a peak wavelength of about 500 to 550 μm), yellow-green (e.g., having a peak wavelength of about 550-575 nm), yellow light (e.g., having a peak wavelength of about 575-595 nm), amber light (e.g., having a peak wavelength of about 595-605 nm), orange light (e.g., having a peak wavelength of about 605-620 nm), red light (e.g., having a peak wavelength of about 620-700 nm), and/or infrared light (e.g., having a peak wavelength of about 700-1200 nm).
In certain embodiments, the LED may emit light having a high power. As previously described, the high power of emitted light may be a result of a pattern that influences the light extraction efficiency of the LED. For example, the light emitted by the LED may have a total power greater than 0.5 Watts (e.g., greater than 1 Watt, greater than 5 Watts, or greater than 10 Watts). In some embodiments, the light generated has a total power of less than 100 Watts, though this should not be construed as a limitation of all embodiments. The total power of the light emitted from an LED can be measured by using an integrating sphere equipped with spectrometer, for example a SLM12 from Sphere Optics Lab Systems. The desired power depends, in part, on the optical system that the LED is being utilized within. For example, a display system (e.g., a LCD system) may benefit from the incorporation of high brightness LEDs which can reduce the total number of LEDs that are used to illuminate the display system.
The light generated by the LED may also have a high total power flux. As used herein, the term “total power flux” refers to the total power divided by the emission area. In some embodiments, the total power flux is greater than 0.03 Watts/mm2, greater than 0.05 Watts/mm2, greater than 0.1 Watts/mm2, or greater than 0.2 Watts/mm2. However, it should be understood that the LEDs used in systems and methods presented herein are not limited to the above-described power and power flux values.
In some embodiments, the LED may be associated with a wavelength-converting region (not shown). The wavelength-converting region may be, for example, a phosphor region. The wavelength-converting region can absorb light emitted by the light-generating region of the LED and emit light having a different wavelength than that absorbed. In this manner, LEDs can emit light of wavelength(s) (and, thus, color) that may not be readily obtainable from LEDs that do not include wavelength-converting regions.
As used herein, an LED may be an LED die, a partially packaged LED die, or a fully packaged LED die. It should be understood that an LED may include two or more LED dies associated with one another, for example a red-light emitting LED die, a green-light emitting LED die, a blue-light emitting LED die, a cyan-light emitting LED die, or a yellow-light emitting LED die. For example, the two or more associated LED dies may be mounted on a common package. The two or more LED dies may be associated such that their respective light emissions may be combined to produce a desired spectral emission. The two or more LED dies may also be electrically associated with one another (e.g., connected to a common ground).
When a structure (e.g., layer, region) is referred to as being “on”, “over” “overlying” or “supported by” another structure, it can be directly on the structure, or an intervening structure (e.g., layer, region) also may be present. A structure that is “directly on” or “in contact with” another structure means that no intervening structure is present.
Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.
This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application Ser. No. 60/801,230, filed on May 16, 2006, which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60801230 | May 2006 | US |
