Abstract:
A solid state lamp includes a mounting area adapted to contain a light emitting diode (LED) chip and a suspension media which physically isolates the diode from the mounting area. The suspension media, while substantially optically transparent, includes suspended phosphor particles for down conversion and scattering of LED emissions. Additionally, the suspension media includes thermal conductivity additives to improve device thermal conductivity in higher power operations.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to the art of solid state lamp assemblies. It finds particular application in conjunction with Light Emitting Diodes (LED&#39;s), and will be described with particular reference thereto. It is to be appreciated, however, that the present invention is also amenable to other types of light emitting semiconductor devices. 
   Solid state lamp assemblies such as LEDs are typically made from a flat chip of material, such as III-V nitrides gallium arsenide, and/or phosphides and silicon carbide, suitably doped with material or designed so as to form a p-n junction which emits light when current is passed therethrough. Indeed, such devices emit light from all exposed surfaces when injected with an appropriate input current. Undesirably however, the light emitted by these devices tends to be of relatively low intensity due to scattering and/or absorption. 
   This inefficiency has been recognized, and effort has been directed towards solving this particular problem. Typical solutions tend to focus the light emanating from the exposed chip surfaces. Exemplary methods of implementation include angling the chip mounting area, frequently a cup, to redirect emitted light, lining the mounting area with a reflective surface, shaping the diode material itself into a lens, or adding a separate lens fixture to the LED. 
   The present invention contemplates a new and improved method and apparatus which helps to reduce certain of the above-referenced problems and others. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with one aspect of the present invention, a solid state lamp includes a light emitting element and a mounting area adapted to contain the element. A suspension media supportably surrounds the element within the mounting area. 
   In accordance with another aspect of the present invention, the suspension media comprises a substantially transparent material. 
   In accordance with another aspect of the present invention, the suspension media includes a first layer disposed between the mounting area and the light emitting diode element, and a second layer covering the light emitting diode element and the first layer. 
   In accordance with another aspect of the present invention, the first layer includes a thermally conductive filler. 
   In accordance with another aspect of the present invention, the first layer includes phosphor particles. 
   In accordance with another aspect of the present invention, the second layer includes phosphor particles. 
   In accordance with another aspect of the present invention, a third layer is supplied and located between the light emitting diode element and the second layer. 
   In accordance with another aspect of the present invention, at least one of the first or second layers includes gold or silver nano-particles. 
   In accordance with another aspect of the present invention, at least one of the first or second layers includes single crystal nano-particles such as diamonds. 
   In accordance with another aspect of the present invention, at least one of the first or second layers includes dielectric nano-particles such as fumed alumina, TiO 2 , SrTiO 3 , etc., to improve thermal conductivity while minimizing optic scattering. 
   In accordance with another embodiment of the present invention, a method of manufacturing a solid state lamp includes locating a suspension media in a mounting area where a volume of the mounting area exceeds a volume of the suspension media. The method further includes disposing a light emitting device on the suspension media. 
   In accordance with another aspect of the present invention, the method further includes affixing electrical leads to the light emitting device. 
   In accordance with another aspect of the present invention, the method further includes depositing a phosphor embedded suspension layer over the light emitting device and the suspension media. 
   In accordance with another embodiment of the present invention, a photonic device includes a mounting area and a spacing element which both spaces a semiconductor device from the mounting area and affixes the semiconductor device within the mounting area. 
   In accordance with another aspect of the present invention, the spacing element comprises an optically transparent media disposed between the mounting area and the semiconductor device. 
   In accordance with another aspect of the present invention, the optically transparent media includes silicone epoxy blended with phosphor particles. 
   In accordance with another aspect of the present invention, the optically transparent media includes silicone epoxy blended with thermally conductive fillers. 
   In accordance with another aspect of the present invention, the spacing element includes an optically transparent media disposed over both the semiconductor device and the spacing element. 
   In accordance with another aspect of the present invention, the photonic device further includes a phosphor layer disposed over the semiconductor device between the spacing element and the means for affixing. 
   One advantage of the present invention resides in an optic buffer or spacer blended with thermally conductive fillers to improve thermal conductivity and the refractive index of the device. 
   Another advantage of the present invention resides in the ability to blend phosphor particles within the suspension media for down conversion and scattering of LED emissions. 
   Yet another advantage of the present invention resides in the surrounding of the LED chip by the suspension media providing a channel for the light output from all surfaces of the chip. 
   Still further advantages and benefits of the invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. 
       FIG. 1  is a cross section of an LED photonic device in accordance with the present invention; 
       FIG. 2  is a cross section of an LED photonic device according to an alternate embodiment of the present invention; and, 
       FIG. 3  is a cross section of an LED photonic device according to an alternate embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIG. 1 , a photonic device  10  such as the LED illustrated includes a metal mount  12  defining a mounting area or cup  14 . A first layer of suspension media  16 , such as silicone epoxy, is deposited into the cup  14 . Those skilled in the art will appreciate that the silicone epoxy  16  can be pure or filled with additives to improve thermal conductivity, to adjust the refractive index, and/or to down convert the emission from an LED and scatter light. The viscosity of the silicone epoxy  16  is adjusted, for example by fillers or mild curing, to an extent that a deposited LED chip will stick to and sit upon the first layer  16  without settling appreciably. At this point, an LED chip  20  is placed upon the first layer  16 . Either an upper face (with an electrode pad), or a bottom face (sapphire) of the LED chip  20  is usable in this configuration as a mounting face. Those skilled in the art will appreciate that if electrical leads were not previously applied to the LED chip  20 , such wiring can now be bonded to the chip and to the electrode legs (not shown). 
   A second layer of silicone epoxy  22  is deposited over the exposed face of the LED chip  20  and the cured first layer  16 . In the illustrated embodiment, the second layer  22  includes suspended phosphor particles blended into the silicon epoxy to improve down-conversion and scattering of LED emissions. A conventional curing process, such as thermal/UV curing, is then performed on the silicone phosphor blend. Those skilled in the art will appreciate that conventional epoxy packaging such as forming a dome shaped epoxy onto the mounted LED, can now occur as desired. 
   With reference now to  FIG. 2 , a floating chip LED  30  includes a metal mount  12  defining an LED mounting area or cup  14 . A first layer of silicone epoxy suspension media  32  is blended with thermally conductive fillers  34  (enlarged for illustration) to improve thermal conductivity for higher power LED operations. In one embodiment, thermal conductivity filler  34  includes blended gold (Au) or silver (Ag) nano-particles which are commercially available. The concentration of gold/silver nano-particles is controlled to enhance the thermal conductivity without shorting the LED circuit. This blend enhances thermal conductivity while not inducing optical scattering due to the nanometer size of the particles  34 . In another embodiment, the thermal conductivity filler  34  can include single crystal or dielectric nano-particles. Exemplary single crystal particles include diamonds, while dielectric particles include various oxides such as fumed alumina, TiO 2 , SrTiO 3 , etc. These nano-particles are also commercially available. These particles contribute to improved thermal conductivity while not inducing optical scattering. The resulting composite layer is still an electric insulator, but the addition of high dielectric constant additives improves the light extraction from the LED by increasing the refractive index of the silicone composite layer  32 . 
   The device  30  also includes an LED chip  20  placed on the first layer  32 . As above, wire bonding can alternately occur prior to placement, or after the first layer  32  has been sufficiently cured. In the illustrated embodiment, a phosphor layer  38  is deposited directly on the upper surface of the LED  20  and over the first layer  32 . Those skilled in the art will recognize that the phosphor layer  38  acts to down convert the light emitted from the LED. A second suspension layer  40 , substantially identical to the first suspension layer  32 , is provided over the phosphor layer  38  to hold the LED chip  20  in place, and improve thermal conductivity by the addition of thermal conductivity fillers  34 . 
   With reference now to  FIG. 3 , an alternate embodiment is illustrated which also increases the surface area from which an LED chip  20 ′ emits light. Substantially as above, a first layer  16  is deposited into an LED cup or lead frame  14 . The first layer  16  is then at least partially cured so that it will support the LED chip  20 ′ within the cup  14 . While the chip  20 ′ is illustrated as being fully suspended within the cup  14 , those skilled in the art will appreciate that the chip  20 ′ can alternately rest on the base of the cup while still providing enhanced efficiency of emitted light. A second layer  22  is then deposited over both the LED chip  20 ′ and the first layer  16  to further support the chip  20 ′ and electrical leads  50 . As above, the suspension media  16 ,  22  may be dispersed with additives to improve thermal efficiency and/or quality of output light. 
   The invention has been described with reference to the preferred embodiments. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.