JP2011176350A - High-efficacy white light-emitting-diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a white light emitting solid-state lamp having an output of at least 75 lumens per watt at a 20-milliampere drive current. <P>SOLUTION: The lamp includes a light-emitting diode 21, an encapsulant, and a header. The diode includes a conductive silicon carbide substrate for electrical contact, and a group III nitride active portion on a silicon carbide substrate for generating a desired frequency of photons under the application of current across the diode. The header includes a reflective cup 22 for supporting the diode and for providing electrical contact to the diode and to the active portion. The encapsulant includes a phosphor 31 and is present in at least a portion of the encapsulant for generating a responsive frequency when the phosphor is excited at the frequency emitted by the diode. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to artificial lighting, and more particularly to a solid state lamp that generates white light.

  Artificial lighting for lighting purposes is incorporated in a wide variety of environments. The main types include office lighting, home lighting, outdoor lighting for various purposes, signals, indicators and the like. In the age of modern electrification, common forms of artificial lighting include (but are not limited to) incandescent lamps, halogen vapor lamps, and fluorescent lamps. All of these have certain advantages and disadvantages, but in certain aspects they all use a relatively large amount of power compared to the light output, and all are clearly limited in use. It seems to have a deadline. In particular, incandescent lamps have been used in the present form for about a century, and are one of the longest remaining modern inventions, leaving the original form. In contrast, most other early electronic technologies have replaced digital electronic technologies.

  The semiconductor era witnessed the replacement of many types of electrical devices with solid state devices. Perhaps the most obvious is the change of vacuum tubes to transistors (which most young people don't know). Solid state devices, by virtue of their nature and operation, are inherently much more reliable than older generation electronic devices, and in general can clearly have a lifetime that is at least 100 times longer.

  In addition, some solid state devices emit light in operation. The most common are light emitting diodes (LEDs), where current is injected across the pn junction, resulting in recombination of electrons and holes, with the simultaneous generation of photons. Depending on the semiconductor material from which the diode is formed and in particular according to the band gap of those materials, different frequencies of light are emitted, which are characteristic of the material. For example, gallium arsenide phosphorus (GaAsP) represents a well-established material system for light emitting diodes. Depending on the molar fraction of Ga and As, these materials have a band gap of about 1.42 to 1.98 electron volts (eV) and emit light in the infrared, red, and orange portions of the electromagnetic spectrum.

  In contrast, materials such as silicon carbide (SiC), gallium nitride (GaN), or related Group III nitride compounds have wider band gaps of about 3.0 and about 3.5 eV, respectively. , Thus producing high frequency photons in the blue, purple, and ultraviolet portions of the spectrum.

  Due to reliability, efficiency and relatively low power requirements, solid state light emitting devices are widely accepted for many applications. However, because the device is relatively small and relatively darker than the more traditional alternatives (incandescent, fluorescent), diodes are most often used for indicators and other than for lighting This is for applications with low luminance.

  Furthermore, some of the LED characteristics that are favorable in many situations (eg, emission along a narrow band of wavelengths) tend to make the LED less attractive initially for illumination purposes. For example, LEDs cast only a narrow range of wavelengths. In many situations this is unfavorable compared to natural light, or even compared to incandescent or fluorescent light, since in many cases much of the color perception depends on the illumination frequency. Because natural light or incandescent light or fluorescent light actually casts light over a wider range of frequencies than LEDs due to their inherent limitations.

  Two types of techniques are used to generate white light from light emitting diodes. First, the blue light emitting diode is combined with the red and green light emitting diodes to produce the desired full color of the visible spectrum including white light. Second, high frequency light emitting diodes (eg in the ultraviolet, purple, blue range) are used with luminescent materials (generally emitting yellow light), so that blue light from the diode and phosphor It emits combined light with yellow light, which in combination provides white light from the lamp.

  The efficiency of light emitting diodes can be characterized in a variety of ways, but in practice it generally depends on several factors that have accumulated good and bad points. For example, for any given amount of current injected into the light emitting diode, some fraction of less than 100% of the injected carriers (electrons or holes) is actually recombined. Another fraction, less than 100% of those that recombine, generates photons. Of the generated photons, yet another fraction of less than 100% is actually extracted. That is, it leaves the diode as visible light. When a phosphor is incorporated, the efficiency is further reduced by the phosphor conversion efficiency.

  Based on these and other factors, full-spectrum light-emitting diode devices have the potential to completely replace both incandescent and fluorescent lamps, but are cheap and easy to manufacture solid-state lamps that emit white light Remains a major subject for both researchers and manufacturers.

  Thus, increasing the desired output of the white light emitting diode for illumination purposes requires increasing one or more of injection efficiency, the rate of radiative recombination, and the amount of photons extracted. . Thus, when used, it is still continuing to produce a more satisfying effect by producing a brighter full output at relative power levels and over a wider range of spectra. Is the goal.

  One aspect of the present invention is a high efficiency, high power white light emitting solid state lamp having an output of at least 75 lumens per watt at an operating current of 20 milliamps. In this aspect, the present invention includes a light emitting diode, a capsule material, and a header. The diode includes a conductive silicon carbide substrate for electrical contact and an active portion of a group III nitride on the silicon carbide substrate for generating photons of a desired frequency under the application of current across the diode. . The header includes a reflective cup for supporting the diode and providing electrical contact to the diode and the active portion. The encapsulating material includes a phosphor that is present in at least a portion of the encapsulating material to generate a response frequency when it is excited by the frequency emitted by the diode.

  In another aspect, the invention is a packaged light emitting diode lamp that exhibits at least 57 lumens of white light per watt at an operating current of 350 milliamps. The lamp includes a conductive header and a light emitting diode on the header. The diode is in resistive contact with a silicon carbide substrate, an active layer of at least one indium gallium nitride, and an active layer in a direction perpendicular to the substrate and the active layer and in electrical contact with the header. Including resistive contacts. The encapsulant covers at least a portion of the diode and header. The phosphor in the capsule material emits visible light in response to light emitted from the diode.

  In another aspect, the invention is a packaged light emitting diode lamp that exhibits at least 142 lumens of white light per watt at an operating current of 1 ampere.

  In another aspect, the invention is a white light emitting diode based lamp, the white light emitting diode based lamp including a light emitting diode, the light emitting diode being selected from the ultraviolet, blue and violet portions of the electromagnetic spectrum. Emits light in the part of the spectrum. The recessed header supports a diode, which has a shape that maximizes the extraction of light from the diode in the recess. The first portion of encapsulating resin covers the diode within the recess but does not fill the remainder of the recess. The second part formed with the mixture of encapsulating resin and phosphor fills the remaining part of the well, thereby separating the phosphor-containing part sufficiently away from the diode, otherwise extracted fluorescence. Prevents the diode from absorbing light from the body. The lens is on a filled indentation and is formed of encapsulating resin to increase and maximize light extraction from the lamp.

  In another aspect, the present invention is a method of forming a high efficiency white light emitting semiconductor-based lamp. In this aspect, the method includes forming a cup-shaped recess in the base of the header to provide electrical contact and a reflective back surface and structure, and placing a high frequency light emitting diode in the recess. Electrically connecting the diode to the insulated leads; partially filling the recessed cup with encapsulating material sufficient to cover the chip without filling the cup; and partially filled Filling the rest of the cup with a mixture of the encapsulating material and the phosphor that responds to the frequency produced by the diode with the encapsulating material, thereby filling the phosphor from direct contact with the diode Separating and thereby minimizing the absorption of phosphorescent light by the diode and curing the remaining encapsulated material in the cup Forming a solid lens of encapsulated material on the cured material in the cup to enhance light extraction from the diode; curing the lens material to form a finished lamp; Including.

  The above and other objects and advantages of the invention and the manner in which the same results are achieved will become more apparent based on the following detailed description taken in conjunction with the accompanying drawings.

FIG. 1 is a schematic cross-sectional view of a portion of a lamp according to the present invention. FIG. 2 is a top view of a die cup for a diode lamp according to the present invention. 3 is a cross-sectional view taken along line 3-3 in FIG. FIG. 4 is a schematic cross-sectional view of a slag lamp package according to the present invention. FIG. 5 is a schematic cross-sectional view of a cup-type lamp package according to the present invention. FIG. 6 is a combined graph of efficiency versus flux for a lamp according to the present invention. FIG. 7 is a color point graph of a CIE diagram of a lamp according to the present invention. FIG. 8 is a graph of wavelength versus intensity for a lamp according to the present invention. FIG. 9 is another graph of current vs. efficiency and flux graphs for a lamp according to the present invention. FIG. 10 is a graph of the CIE color point of a lamp according to another embodiment of the present invention. FIG. 11 is a version of each of the CIE diagrams. FIG. 12 is a version of each CIE diagram.

  The present invention is a highly efficient white light emitting solid state lamp. A lamp according to the invention is characterized by an output of at least 75 lumens per watt (W) at a drive current of 20 milliamps (mA).

  The units of measurement reported herein are conventional and well understood. Therefore, the measured light flux is a unit of photometric measurement and is measured in lumens. Although not identical, the corresponding radiometric measurement is the radiant flux measured in watts. In this specification, efficiency is shown as luminous flux in watts based on the current across the diode, most often in milliamps.

  The term “external quantum efficiency” is used to describe the ratio of emission intensity to current flow (eg, outgoing photons / incoming electrons). Photons are lost by absorption in the semiconductor material itself, when light passes from the semiconductor to the air, it is lost through loss of reflected light due to the difference in refractive index, and an angle greater than the critical angle defined by Snell's law Can be lost due to internal reflection of light. Thus, the external quantum efficiency (EQE) as a percentage is the radiant flux (watts), wavelength (nanometers), drive current (amperes), and wavelength and energy (λ = 1.24 / eV) according to the following equation: Can be calculated from the conversion factor between:

発光ダイオードおよびランプに関するこれらまたは他の要素の有益な短い概要が、Ｌａｂｓｐｈｅｒｅ， Ｉｎｃ． Ｎｏｒｔｈ Ｓｕｔｔｏｎ Ｎｅｗ Ｈａｍｐｓｈｉｒｅからのｔｈｅ Ｌａｂｓｐｈｅｒｅ Ｔｅｃｈｎｉｃａｌ Ｇｕｉｄｅ、「Ｔｈｅ Ｒａｄｉｏｍｅｔｒｙ ｏｆ Ｌｉｇｈｔ Ｅｍｉｔｔｉｎｇ Ｄｉｏｄｅｓ」に述べられている。

A useful short overview of these or other elements for light emitting diodes and lamps is provided by Labsphere, Inc. The Labsphere Technical Guide from North Sutton New Hampshire, “The Radiometry of Light Emitting Diodes”.

  In a first embodiment, the lamp includes a light emitting diode (also referred to as a “die” or “chip”), an encapsulant, and a header. The diode includes a conductive silicon carbide substrate for electrical contact and a group III nitride active portion on the silicon carbide substrate for generating photons of a desired frequency under application of current across the diode. .

The header includes a reflective cup for supporting the diode and for providing an electrical contact between the diode and the active part.
When the phosphor is excited by the frequency emitted by the diode, at least a portion of the encapsulant includes a phosphor for generating a response frequency in the visible wavelength range.

  FIG. 1 is a schematic diagram illustrating some of these features. In FIG. 1, the diode is schematically indicated at 20. The light emitting diode is indicated generally at 21 and is located in a recess (or cup) 22 in the header 24, which is best illustrated in FIG. FIG. 2 illustrates these elements from above. The recess 22 has a functional shape that maximizes the extraction of light from the diode 21. In a preferred embodiment, the indentation 22 has a frustoconical shape. That is, the circular floor faces the larger parallel circular opening 26 and has an inclined wall 27 between the opening 26 and the floor 25. Although the exact angle of the wall 27 can be selected and designed to maximize light extraction from the individual chip design, in the present invention the wall is most preferably about 45 relative to the floor 25. Arranged at an angle between 60 degrees and 60 degrees. In a preferred embodiment, the recessed cup 22 is coated with a reflective metal, most preferably silver (Ag).

  In the embodiment of the invention illustrated in FIG. 1, the encapsulant has three parts. The first portion of the capsule material is typically an epoxy resin and is indicated at 30 and fills some but not all of the cup 22. In particular, the first portion covers and extends over the diode 21. The second portion of the capsule material 31 is formed of a mixture of a resin (usually the same resin for optical purposes) and a phosphor. This second part fills the remaining part of the cup 22, thereby sufficiently separating the phosphor-containing part 31 from the diode 21, thereby reducing the amount of fluorescent emission absorbed (and thus wasted) by the diode. Minimize.

  In other words, with respect to light emission from the phosphor, the diode is simply an obstacle to the emitted light. Keeping the diode away from the phosphor minimizes this unwanted effect that would otherwise occur.

  The third portion of the encapsulant 32 forms a lens, often hemispherical, on the filled cup 22 to maximize and increase light extraction from the lamp.

  In certain embodiments of the invention, the lamp 20 is at least 75 lumens per watt at 20 milliamps of drive current, and in some cases 80 lumens per watt at 20 milliamps of drive current. In some cases, an output of at least 85 lumens per watt can be produced at a drive current of 20 milliamps.

  At other drive currents, the diode according to the present invention exhibited at least 57 lumens of white light per watt at an operating current of 350 milliamps and also exhibited at least 142 lumens of white light per watt at an operating current of 1 ampere. .

  In addition to the structure of the capsule material, the present invention takes advantage of specific achievements described in more detail in patents, published applications, and co-pending applications. Cited in the specification and incorporated by reference.

  In a preferred embodiment, diode 21 includes, but is not limited to, Cree Inc., the assignee of the present invention. Of the XT290 and XB900 series light emitting diodes available from Durham North Carolina. These diodes include a conductive silicon carbide substrate, illustrated at 33 in FIG. 1, which includes at least one p-type III-nitride layer 34 and at least one n-type n-type. Group III nitride layer 35, preferably combined with InGaN. One resistive contact 36 is made on the silicon carbide substrate 33 and another resistive contact 37 is made on the appropriate group III nitride layer.

  The XT290 chip has a 300 × 300 micron (μ) footprint with a thickness of approximately 115 μ. The XB900 chip is clearly large and has a 900 × 900μ footprint and about 250μ thickness. Thus, although the term is used somewhat arbitrarily, the XB900 chip represents a more “powered” design. Like between two chips in commercial use, the larger sized XB900 chip is an attractive candidate for general lighting, including work lighting, outdoor lighting, and signal colors, and the smaller XT290 chip. Is beneficial for low voltage applications such as backlights in cell phones, digital cameras, instrument lights, indicator lights in audio and video devices.

  From a performance standpoint, the XB900 series can operate at a forward current of 400 milliamps with a peak forward current of 500 milliamps, while the smaller XT290 chip has a maximum forward current rating of 30 milliamps and a 100 milliamp. Peak forward current.

  In the preferred embodiment, and like the exemplary XT290 and XB900 series chips, the chip 21 is in a “flip chip” direction, in which the substrate 33 is in an upward direction. Facing (towards the lens 32), the active layers 34 and 35 are adjacent to the cup 22. As stated in some incorporated references, this design can help increase light extraction. In the preferred example, due to the characteristics of silicon carbide, the silicon carbide substrate is typically n-type, as is the adjacent group III nitride layer 35. Next, another Group III nitride layer 34 is p-type and forms a pn junction to inject current and recombine carriers. When the substrate is n-type (common but not exclusive), p-type layer 34 contacts resistive contact 37 and then contacts cup 22. Lead wires 40 and 41 are schematically included in the drawings to show the means for external connection with other devices or circuits.

  Those skilled in the art who are familiar with the detailed structure of light emitting diodes will understand that “on” describes the structural elements (typically semiconductor or metal layers) that are in direct contact with each other. The same is true for structures that include intermediate layers or structures that help enhance the overall functionality of the device. Thus, even though it is described herein as “on” a silicon carbide substrate, the Group III nitride layer is often the electronic and crystalline structure between the substrate and the active layer. With a buffer layer that enhances both transitions. Similarly, the p-type layers of these diodes are generally formed of two parts, one part being relatively suitable for strengthening the resistive contact between the semiconductor and the metal, The metal forms a contact.

  Furthermore, although the basic structure of a light emitting diode is based on p-type and n-type layers, it should be appreciated by those skilled in the art that a layer can include multiple arrangements, such as multiple quantum wells and superlattice structures. That is. In order to accurately describe the present invention, it should be understood that these features may be incorporated into the present invention but are not described in detail herein.

  In a more preferred embodiment, diode 21 includes resistive contacts 36 and 37 and has an overall size of only about 250 microns (μ). In a more preferred embodiment, these dimensions are only about 100 microns. These thin chips offer certain advantages in light extraction geometries for lighting purposes and for use in small displays such as mobile phones, digital cameras and mobile terminals.

  As a further method of reducing the size of chip 21 and increasing light extraction, the present invention incorporates a thin resistive contact, which preferably has an average thickness of about 1-250 Angstroms ( Å), most preferably between about 1-10 Å.

  White light is a combination of other colors, and the diodes used in the lamps of the present invention typically emit in the ultraviolet, violet, and blue portions of the electromagnetic spectrum, so the ultraviolet, purple, and violet wavelengths of the electromagnetic spectrum. When excited by light emitted from the diode in the blue part, the phosphor contained in the second resin part 31 is selected to emit a response frequency in the yellow part of the visible spectrum.

Cesium yttrium aluminum garnet (“Ce: YAG”, Y ₃ Al ₅ O ₁₂ : Ce ⁺³ ) is a suitable phosphor for this purpose. Other materials including yellow / green emitting phosphors that respond to diodes that are useful in the present invention include, but are not limited to, US Pat. Appl. No. US 2004/0012027, paragraphs 51-69 and 74- 75.

  The amount of phosphor mixed with the encapsulant can be determined by one skilled in the art without undue experimentation. As is generally recognized in the art, the goal is to maximize the amount of light that is converted, but at the same time minimize the amount of light that is only blocked by the phosphor, and the structural integrity of the encapsulant. Is to avoid disturbing. An appropriate amount can be selected by one skilled in the art without undue experimentation.

  Further, the physical size of the phosphor particles can affect (advantageously or unfavorably) the efficiency of both the phosphor conversion of light from the diode and the extraction of phosphorescent light from the lamp package. . In preferred embodiments of the present invention, the size of the phosphor particles can be selected by one skilled in the art without undue experimentation, but preferably the average size range is about 0. Between 001 and 20 microns.

  If desired, the encapsulant may also include a scattering material, and the nature and function of the scattering material is generally well understood in the art. Related descriptions are set forth in paragraphs 101 and 102 of US Patent Application Publication No. 2004012027.

  FIG. 8 is a spectrum obtained from a diode according to the present invention, showing the emission of the diode at about 455 nanometers (nm) and the relatively broad range (about 490-700 nm) emitted by the phosphor. Show.

  2 and 3 illustrate the top surface and cross-section of the header 24 and the cup 25. FIG. With particular reference to FIG. 3, in the exemplary embodiment, floor 25 has a diameter of about 0.064 inches (0.163 cm) and opening 26 has a diameter of about 0.124 inches (0.315 cm); The depth of the cup 22 is approximately 0.030 inches (0.76 cm) and the wall 27 is oriented at an angle of 45 degrees. The outer dimensions of the header 24 are not very important. This is because the phosphor layer is almost maintained in the cup 22. However, a T039 transistor type header has been found to be sufficient to carry the recessed cup 22. To obtain proper placement of the chip 21, the floor 25 should have a flatness of 0.001 and all dimensional tolerances should be within 0.005 inches (0.013 cm). . An iron-nickel-cobalt alloy, such as Kovar®, is (but is not limited to) an exemplary material for the header.

  4 and 5 are further cross-sectional schematic views of a lamp according to the present invention. FIG. 4 illustrates a slag type package, indicated generally at 44. While the encapsulant is understood to form the same three parts as shown in greater detail in FIG. 1, the encapsulant is shown as a single part 45. The diode is also generally indicated at 21, the cup is generally indicated at 22, and the header is indicated at 24. FIG. 4 also illustrates lead wires 40 and 41.

  FIG. 5 schematically illustrates a cup-type package, indicated generally at 47, in which the encapsulating material 50 completely surrounds the header cup, which is indicated at 51 for the purpose of distinction. Yes. It should also be understood that the encapsulant 50 is formed of three parts, the first part in the cup covers the diode 21, the second part fills the rest of the cup, and the phosphor The third part is to form a lens. Similar to FIGS. 1 and 4, FIG. 5 also illustrates electrical lead wires 40 and 41.

  6-10 illustrate some performance characteristics of diodes and lamps according to the present invention. 6, 7 and 8 depict data for a high efficiency XT290 based white lamp according to the present invention, and FIGS. 9 and 10 depict similar data for an XB900 based white lamp according to the present invention. I'm drawing.

  FIG. 6 depicts two different ordinates for a common abscissa. The left ordinate shows effectiveness (efficiency) in lumens per watt, plotted with open squares and connecting lines. The ordinate on the right shows the output flux measured in lumens, plotted with black diamond shapes and connecting lines. Since each line is drawn for two different ordinates, the clear convergence of the lines in FIG. 6 has no particular meaning.

  FIG. 7 is a graph of the emission of a plurality of white light-emitting lamps according to the present invention, drawn using the x and y axes from the CIE color chart (FIGS. 11 and 12). All of the lamps have an efficiency of 75 lumens per watt and are shown compared to the blackbody curve.

  As indicated above, FIG. 8 is a graph of intensity in arbitrary units versus wavelength in nanometers (nm) for a lamp according to the present invention. FIG. 8 illustrates the emission of the diode with a characteristic sharp peak at 455 nanometers and the relatively broad emission of the phosphor over the frequency range between about 500-700 nm.

  FIG. 9 is a graph similar to FIG. 6 except that it is obtained from a lamp using XB900. FIG. 9 also accidentally depicts lumens (dark squares) and lumens per watt (black diamond shape) on the same axis. Therefore, the intersection of two graphs is also a coincidence.

  FIG. 10 is a graph similar to FIG. 7, except that a larger footprint XB900 diode is used. FIG. 10 also compares the white light output from the lamp according to the invention in comparison with the CIE coordinate point and the blackbody curve.

  FIG. 11 (Luminal Path Corporation, www.photo.net) and FIG. 12 (Graphics, FS Hill) are representative versions of a CIE color chart with blackbody radiation curves superimposed on FIG. FIG. 12 is useful from a graphic point of view. This is because various colors are drawn with lines and characters rather than shaded areas.

  In yet another aspect, the present invention is a method of forming a high efficiency white light emitting semiconductor based lamp. In this aspect, the method includes providing an electrical contact and a reflective background structure by forming a cup-shaped recess in the header. A high frequency light emitting diode emitting in the high frequency range (ultraviolet, purple, blue) is placed in the recess and makes electrical contact with the insulated leads.

  Second, the recessed cup is sufficient to cover the chip, but the cup does not fill the (clear / transparent / suitable) encapsulant (usually colorless and at most visible frequencies) Partly filled). The partially filled encapsulant material is cured, followed by filling the remainder of the cup with a mixture of encapsulant material and phosphor that responds to the frequency generated by the diode. This separates the phosphor from direct contact with the diode, thereby minimizing absorption of the fluorescent light during operation by the diode. The remaining encapsulated material in the cup is cured, followed by the formation of a three-dimensional geometric solid lens of encapsulated material on the cured material in the cup. The lens material is then cured to form the finished lamp.

  As in the device aspect of the present invention, the diode disposed in the cup preferably includes at least a conductive silicon carbide substrate and at least one active portion of a group III nitride in a vertical direction.

The term “vertical” is used herein in the conventional sense with respect to light emitting diodes, meaning that a resistive contact to the device may be located at the opposite end of the device. The usefulness of the conductive silicon carbide substrate allows a vertical arrangement that is generally more suitable for practical use of light emitting diodes, and the vertical arrangement is on a nonconductive substrate such as sapphire (Al ₂ O ₃ ). There is also a need for similar diodes formed in When using a non-conductive substrate, the respective resistive contacts to the p-type and n-type portions of the diode should be placed side-by-side in some type, and as a result The diode footprint increases. And, in addition to other disadvantages, increasing the footprint reduces the output of the diode per unit area.

  In order to enhance light extraction, an aspect of the method of the present invention incorporates etching the surface of the silicon carbide substrate opposite the Group III nitride layer, the method comprising aqueous etching. Use to remove the damaged portion of the substrate, thereby increasing the extraction of light from the resulting diodes and lamps.

  The resin used for encapsulation in each step is preferably an epoxy resin, and the epoxy resin has a refractive index greater than 1.0, more preferably a refractive index greater than 1.5. As is generally known to those skilled in the optical field, particularly those familiar with light emitting diodes and lamps, the lens material has a refractive index greater than air, so that the lens is more from the diode than if the diode is in contact with air. Extract the light.

The lens structure can also be modified in the manner described in commonly assigned US Pat. No. 6,791,119.
If desired or necessary, the capsule material may be installed and formed of the material described in co-pending US Patent Application Publication No. 2004/0227149 by the same applicant.

The diode portion of the lamp according to the present invention may also incorporate the improved current spreading structure described in commonly assigned US Pat. No. 6,614,056.
The main component of the present invention is the performance of the blue (455-465 nm) LED chip, and the wall plug efficiency (combination of external quantum efficiency and voltage) of the blue LED chip is described herein. It must be high enough to achieve the performance of the white lamp that is being used. For a 300 μx 300 μ chip operating at 20 mA, typical external quantum efficiencies and voltages are 44% and 3.1 V, respectively. For a 900 μx 900 μ chip operating at 350 mA, typical external quantum efficiencies and voltages are 31% and 3.2 V, respectively. In both cases, the data is for packaged (encapsulated) chips.

  As referred to herein, the wall plug efficiency of an LED is the LED injection efficiency (ratio of the number of carriers injected into the device relative to the number of carriers recombined in the device's light generation region) and the LED's Luminous efficiency (ratio of recombination of electron holes that led to the light emission phenomenon relative to the total number of recombination of electron holes) and extraction efficiency of LED (ratio of photons extracted from LED to the total number of photons formed) Is the result. The wall plug efficiency of a device is also defined as the ratio of the optical wattage output from the device to the electrical wattage passed through the device.

(Experiment)
The XT290 chip was placed on a silver plated T039 header. The cup-shaped depression was machined to become the base of the header, and the chip was placed in the center of the depression base. After the wire is bonded to the insulated lead, the cup is partially filled with a clear encapsulant that covers the chip but does not fill the cup. A clear epoxy of OS 1600 (Henkel LocTite Corporation, Rocky Hill Connecticut) was used for encapsulation, and the epoxy reflectivity was about 1.5. After the first cure, the remaining portion of the cup is filled with a mixture of Ce: YAG phosphor (PhosphorTech Corporation Lithia Springs, GA 30122) and OS 1600 epoxy, and continues to the second cure. The concentration of Ce: YAG phosphor was chosen to produce a color point close to a blackbody curve. The header is then placed with the chip facing down in a hemispherical mold filled with more OS1600 epoxy, and then continues to the third and final cure. The completed lamp is characterized by being a 10 inch sphere (Labsphere), and the completed lamp corresponds to a light source derived from NIST. At a drive current of 20 mA, the luminous flux of the lamp exceeds 5 lumens and has an efficiency of 75 lumens or more per watt.

  In the second test, the XB900 chip was placed on a silver plated T039 header. The cup-shaped depression was machined to become the base of the header, and the chip was placed in the center of the depression base. After the wire is bonded to the insulated lead, the cup is partially filled with a clear encapsulant that covers the chip but does not fill the cup. OS1600 clear epoxy was used for encapsulation. After the first cure, the remaining portion of the cup is filled with a mixture of Ce: YAG phosphor and OS1600 epoxy and continues to the second cure. The header is then placed with the chip facing down in a hemispherical mold filled with more OS1600 epoxy, and then continues to the third and final cure. The concentration of Ce: YAG phosphor was chosen to produce a color point close to a blackbody curve. The header is then placed with the chip facing down in a hemispherical mold filled with more OS1600 epoxy, and then continues to the third and final cure. The finished lamp is characterized in that it is a 10 inch perfect sphere. At a drive current of 350 mA, the luminous flux of the lamp exceeds 60 lumens and has an efficiency of 50 lumens or more per watt.

  In the third test, the XT290 chip was placed in a standard 5 mm leadframe cup. The phosphor and encapsulating material were added to the header lamp in the same way. Following the second cure, the lead frame was placed in a bullet shaped mold and overmolded with a clear encapsulant. The luminous efficiency of such a lamp exceeded 75 lumens per watt.

  In the drawings and specification, preferred embodiments of the invention are described, and specific terms are used, but they are used in a schematic and descriptive sense only and are used for limiting purposes. Rather, the scope of the invention is defined in the claims.

Claims (35)

A light emitting diode, a capsule material, and a header,
The diode includes a conductive silicon carbide substrate for electrical contact;
An active portion of a group III nitride on the silicon carbide substrate for generating photons of a desired frequency under application of current across the diode;
The header includes a reflective cup for supporting the diode and providing electrical contact to the diode and the active portion;
The encapsulant includes a phosphor, and the phosphor is present in at least a portion of the encapsulant to generate a response frequency when excited by the frequency emitted by the diode; And a header,
A white light emitting solid state lamp having an output of at least 75 lumens per watt at a drive current of 20 milliamps.   The solid state lamp of claim 1 having an output of at least 80 lumens per watt at a drive current of 20 milliamps.   The solid state lamp of claim 1 having an output of at least 85 lumens per watt at a drive current of 20 milliamps. A conductive silicon carbide substrate having a single polytype;
At least one p-type group III nitride layer on the substrate;
The solid-state lamp of claim 1, comprising: at least one n-type group III-nitride layer on the substrate in a vertical direction.   The solid state lamp of claim 1, comprising a resistive contact to one of the group III nitride layers, wherein the resistive contact is in physical and electrical contact with the header.   The solid state lamp according to claim 1, wherein the capsule material includes an epoxy resin.   The solid state lamp of claim 1, wherein the phosphor emits a response frequency in the yellow portion of the visible spectrum when excited by a frequency emanating from the group consisting of the ultraviolet, purple and blue portions of the electromagnetic spectrum.   The solid state lamp according to claim 7, wherein the phosphor includes cesium yttrium aluminum garnet.   The resistive contact of claim 1, comprising at least one p-type Group III nitride layer and a resistive contact to the p-type layer, the resistive contact having an average thickness of about 1 to 250 mm. Solid state lamp.   The solid state lamp of claim 9, wherein the resistive contact has an average thickness of about 1 to 10 mm. A white light emitting diode based lamp,
A light emitting diode that emits in a portion of the spectrum selected from the ultraviolet, blue and violet portions of the electromagnetic spectrum;
A recessed header supporting the diode, the recess having a shape that maximizes light extraction from the diode in the recess;
A first portion of encapsulating resin that covers the diode within the recess and fills the recess to the extent necessary to cover the diode;
Formed by a mixture of the encapsulating resin and phosphor, filling the remaining part of the well, thereby sufficiently separating the phosphor-containing part from the diode, otherwise extracted. A second portion that minimizes absorption by the diode of light from the possible phosphor;
A white light emitting diode based lamp comprising: a lens on the filled indentation formed of the encapsulating resin to increase and maximize the extraction of the light from the lamp.   12. The diode-based lamp of claim 11, comprising a resistive contact to a p-type group III nitride layer, the resistive contact having an average thickness of about 1-250 inches.   The diode-based lamp of claim 12, wherein the resistive contact has an average thickness of about 1-10 mm.   12. The diode-based lamp of claim 11, wherein the diodes are only about 250 microns in overall size between them including any resistive contacts.   The diode-based lamp of claim 11, wherein the diodes are only about 100 microns in overall size between them including any resistive contacts.   12. The diode-based lamp of claim 11, wherein the light emitting diode comprises at least a silicon carbide substrate and a group III nitride active portion.   The diode comprises a single crystal silicon carbide substrate, at least one p-type group III nitride layer, and at least one n-type group III nitride layer in a vertical direction. The diode-based lamp of claim 16.   The diode-based lamp of claim 16, wherein the diode is disposed in a flip-chip direction on the header.   12. A lamp according to claim 1 or claim 11, wherein the diode emits in a portion of the spectrum selected from the ultraviolet, violet and blue portions of the electromagnetic spectrum.   The diode-based lamp of claim 11, wherein the header is plated with a reflective metal.   21. A lamp according to claim 1 or claim 20, wherein the header is plated with silver.   The lamp according to claim 11, wherein the first portion of the encapsulating resin, the second portion of the encapsulating resin, and the lens are all formed of an epoxy resin.   The diode-based lamp of claim 11, wherein the phosphor emits light in the yellow portion of the visible spectrum in response to light emitted by the diode.   24. The diode-based lamp of claim 23, wherein the phosphor comprises cesium yttrium aluminum garnet.   The diode-based lamp of claim 11, comprising a slug-type package.   The diode-based lamp of claim 11, comprising a cup-type package. A packaged light emitting diode lamp,
A conductive header;
A light emitting diode on the header, wherein the substrate is in electrical contact with the silicon carbide substrate, at least one indium gallium nitride active layer, and in a direction perpendicular to the substrate and the active layer; A light emitting diode comprising a resistive contact in resistive contact with the active layer;
Encapsulant covering at least a portion of the diode and the header;
A phosphor in the capsule material that emits visible light in response to light emission from the diode, and
A packaged light emitting diode lamp wherein the packaged diode exhibits at least 57 lumens of white light per watt at an operating current of 350 mA. A packaged light emitting diode lamp,
A conductive header;
A light emitting diode on the header, wherein the substrate is in electrical contact with the silicon carbide substrate, at least one indium gallium nitride active layer, and in a direction perpendicular to the substrate and the active layer; A light emitting diode comprising a resistive contact in resistive contact with the active layer;
Encapsulant covering at least a portion of the diode and the header;
A phosphor in the capsule material that emits visible light in response to light emission from the diode, and
A packaged light emitting diode lamp wherein the packaged diode exhibits at least 142 lumens of white light per watt at an ampere of operating current. A method of forming a highly efficient white light emitting semiconductor-based lamp, the method comprising:
Forming a cup-shaped recess in the base of the header to provide electrical contact and a reflective background and structure;
Placing a high frequency light emitting diode in contact with the header in the recess;
Partially filling the recessed cup with an amount of encapsulating material sufficient to cover the diode but not fill the cup;
Curing the partially filled encapsulant;
A mixture of the encapsulating material and a phosphor responsive to the frequency generated by the diode fills the remainder of the recessed cup, thereby separating the phosphor from direct contact with the diode. Minimizing the absorption of phosphorescent light by the diode;
Curing the remaining encapsulating material in the recessed cup;
Forming a solid lens of encapsulating material on the cured material in the cup to enhance light extraction from the diode;
Forming a finished lamp by curing the lens material.   Including disposing a high frequency light emitting diode within the recessed cup, the recessed cup including at least a conductive silicon carbide substrate and at least one active portion of a group III nitride in a vertical direction. 30. The method of claim 29.   Etching the surface of the silicon carbide substrate, wherein the silicon carbide substrate uses aqueous etching to remove damaged portions of the substrate, thereby extracting light from the resulting diodes and lamps. 32. The method of claim 30, wherein the method is opposite to at least one Group III nitride layer to be increased.   30. The method of claim 29, wherein filling the recessed cup with an encapsulating material comprises filling the cup with an epoxy resin.   30. The method of claim 29, wherein filling the recessed cup with an encapsulating material comprises filling the cup with a material having a reflectivity greater than 1.0.   Filling the remainder of the recessed cup with a mixture of the encapsulating material and the phosphor includes filling the cup with a mixture, the mixture comprising the ultraviolet, purple and blue portions of the spectrum. 30. The method of claim 29, comprising a phosphor that emits in the yellow portion of the visible spectrum in response to light having a frequency selected from.   35. The method of claim 34, comprising filling the remainder of the recessed cup with a mixture of encapsulating material and cesium yttrium aluminum garnet (Ce: YAG) phosphor.

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