Patent Publication Number: US-2006006793-A1

Title: Deep ultraviolet used to produce white light

Description:
BACKGROUND  
      A conventional single chip light-emitting diode (LED) emits a monochromatic color with high purity. Typical colors emitted are pure blue, pure green, pure yellow or pure red. A white LED is produced by incorporating a photoluminescent material called phosphor together with the LED chip.  
      Typically to produce white light a blue InGaN LED is used with yttrium-aluminum-garnet (YAG) based phosphors, variations of YAG based phosphors, terbium-yttrium-aluminum-garnet based phosphors or variations of terbium-yttrium-aluminum-garnet based phosphors. The peak wavelength emitted for the blue LEDs typically range from 460 nanometers (nm) to 480 nm.  
     SUMMARY OF THE INVENTION  
      In accordance with embodiments of the present invention, a light-generating device includes a light-emitting device emitting light with a wavelength in the range of 160 nm to 290 nm. White light emitting phosphor material is placed in proximity of the light-emitting device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a P-up type die configuration for a deep UV light-emitting device as used with an embodiment of the present invention.  
       FIG. 2  shows a P-N type die configuration for a deep UV light-emitting device as used with an embodiment of the present invention.  
       FIG. 3  shows a P-N flip chip type die configuration for a deep UV light-emitting device as used with an embodiment of the present invention.  
       FIG. 4  shows a white light source that includes a light-emitting device, surrounded by an epoxy that includes phosphor, packaged as a through-hole lamp in accordance with an embodiment of the present invention.  
       FIG. 5  shows a white light source that includes a deep UV light-emitting device, surrounded by an epoxy that includes phosphor, shown used in a high power printed circuit board (PCB) surface mount application in accordance with another embodiment of the present invention.  
       FIG. 6  shows a white light source that includes a deep UV light-emitting device, surrounded by an epoxy that includes phosphor, packaged in a lead frame surface mount application in accordance with another embodiment of the present invention.  
       FIG. 7  shows a white light source that includes a deep UV light-emitting device, surrounded by an epoxy that includes phosphor, mounted within a PCB in accordance with another embodiment of the present invention.  
    
    
     DESCRIPTION OF THE EMBODIMENT  
      In disclosed embodiments of the present invention, deep ultraviolet (UV) light-emitting diodes (LEDs) that emit light with a wavelength in the range of 160 nm to  290  nm and a typical maximum LED chip output of 50 milliwatts, used in conjunction with phosphor material, emit an efficient white light. The use of deep UV provides good color point repeatability and an excellent color rendering index (CRI) of greater than 90. The use of deep Uw also allows better color matching for the white light emitted.  
      In various embodiments of the present invention, a deep UV solid state semiconductor chip is mounted in a cavity in a substrate with a reflective surface. A phosphor material is placed in direct contact or proximity with the light-emitting surface. The light emitted from the chip substrate passes thru the phosphor interface, where the emitted deep UV wavelength is used to excite the phosphor material to produce a secondary emission of white light. The phosphor material can be placed in contact with the Deep UV LED in a coated form, dispersed in a matrix or colloidal paste or a powder conformably coated. The solid state semiconductor deep UV LED can be a single or plurality of chips in a P-up, N-up, P-up and N-up (P-N) or flip chip type die configuration with the reflecting mirror either below or above the emitting active layer depending on the orientation of the emitting active layer. The wavelength emitted by the deep UV LED may range from 160 nm through 290 nm.  
       FIGS. 1 through 3  illustrate the variety of die configurations for deep UV LEDs. These are meant to be illustrative of the wide applicability of the present invention in various configurations, and are not meant to be limiting of the scope of the present invention. For more description on die configurations, see for example, G. B. Stringfellow &amp; M. George Crawford, “High Brightness Light Emitting Diodes”, Semiconductors and Semimetals, vol. 48, Academic Press, 1997.  
       FIG. 1  shows a P-up type die configuration for a deep UV light-emitting device. A layer  101  is composed of N-type contact material. For example, layer  101  is composed of gold-zinc (Au—Zn). A layer  102  is a buffer tie layer. A layer  103  is, for example, an N-doped layer consisting of gallium-nitrogen (GaN) and is, for example, approximately 100 to 180 micrometers (μm) thick. A layer  104  forms a Bragg refractor. For example, layer  104  is approximately 1.5 to 2.0 nanometers (nm) thick. A layer  105  is, for example, an N-doped layer consisting of GaN. A layer  106  is an N-doped layer approximately 15 to 20 μm thick. A layer  107  is, for example, an active layer. For example, layer  107  is approximately 2 to 20 nanometers thick. A layer  108  is, for example, a P-doped layer of GaN. For example, layer  108  is 30 to 50 μm thick. For example, region  109  is composed of P-contact metal such as nickel-gold (Ni—Au) or aluminum (Al). Arrows  110  show illustrative light paths.  
       FIG. 2  shows a P-up and N-up (P-N) type die configuration for a deep UV light-emitting device. A layer  111  is a substrate of variable thickness and composed of, for example, silicon. A layer  112  is a buffer tie layer. A layer  113  is, for example, an N-doped layer consisting of GaN. Region  114  is composed of N-contact metal material such as titanium-aluminum (Ti—Al) or Au—Zn. A layer  115  is, for example, an N-doped layer consisting of GaN and is, for example, approximately 100 to 180 micrometers (μm) thick. A layer  116  forms a Bragg refractor. For example, layer  116  is approximately 1.5 to 2.0 nanometers (nm) thick. A layer  117  is an N-doped layer approximately 15 to 20 μm thick. A layer  118  is, for example, an active layer. For example layer  118  is approximately 2 to 20 nanometers thick. A layer  119  is, for example a P-doped layer of GaN. For example, layer  119  is 30 to 50 μm thick. Region  120  is composed of P-contact metal such as nickel-gold (Ni—Au) or gold-germanium (Au—Ge). Arrows  121  show illustrative light paths.  
       FIG. 3  shows a P-up and N-up (P-N) which is also a flip chip type die configuration for a deep UV light-emitting device. A layer  131  is a substrate of variable thickness and composed of, for example, sapphire. A layer  132  is a buffer tie layer. A layer  133  is, for example, an N-doped layer consisting of GaN. Region  134  is composed of N-contact metal material such as Ti—Al or Au—Zn. A layer  135  is, for example, an N-doped layer consisting of GaN and is, for example approximately 100 to 180 micrometers (μm) thick. A layer  136  is an N-doped layer approximately 15 to 20 μm thick. A layer  137  is, for example, an active layer. For example layer  137  is approximately 2 to 20 nanometers thick. A layer  138  is, for example, a P-doped layer of GaN. For example, layer  138  is 30 to 50 μm thick. Region  139  is composed of P-contact metal such as Ni—Au or Au—Ge. Arrows  140  show illustrative light paths.  
       FIG. 4  shows a through-hole lamp that includes a liquid encapsulation epoxy  13 , a pin  14  and a pin  15 . A light-emitting device  11  is mounted within a reflective cup area  10  of the through-hole lamp. Light-emitting device  11  is covered by an epoxy  12  that includes phosphor material. For example, epoxy  12  is a liquid epoxy that includes a YAG based phosphor, a variation of YAG based phosphor, a terbium-aluminum-garnet (TAG) based phosphors or a variation of TAG based phosphors. Other phosphor blends may also be used. See, for example, U.S. Pat. No. 6,621,211 B1. For example light-emitting device  11  is a deep UV light-emitting diode (LED) that emits light with a wavelength within a range of 160 nm to 290 nm. Alternatively, the phosphor material may be located in other locations, such as somewhere within encapsulation epoxy  13  or on a shell surrounding encapsulation epoxy  13 .  
       FIG. 5  shows a light-emitting device  52  placed in a surface mount configuration within a reflective cup area  50  of a PCB  51 . A wire  53  is connected between light-emitting device  52  and PCB  51 . Epoxy  54  includes phosphor material. For example, epoxy  54  is a liquid epoxy that includes a YAG based phosphor, a variation of YAG based phosphors, a TAG based phosphor or a variation of TAG based phosphors. Other phosphor blends may also be used. A mold compound  55  is placed over epoxy  54 . For example, light-emitting device  52  is a deep UV light-emitting diode (LED) that emits light with a wavelength within a range of 160 nm to 290 nm.  
       FIG. 6  shows a light-emitting device  63  placed in a surface mount configuration on a leadframe portion  61 . A wire  64  is connected between light-emitting device  63  and leadframe portion  61 . A wire  65  is connected between light-emitting device  63  and a leadframe portion  62 . Epoxy  66  includes phosphor material. For example, epoxy  66  is a liquid epoxy that includes a YAG based phosphor, a variation of YAG based phosphors, a TAG based phosphor or a variation of TAG based phosphors. Other phosphor blends may also be used. For example, light-emitting device  63  is a deep UV light-emitting diode (LED) that emits light with a wavelength within a range of 160 nm to 290 nm.  
       FIG. 7  shows a light-emitting device  75  mounted on a heat sink  74  within a reflective cup area  70  of a PCB substrate  71 . Vias  72  through PCB substrate  71  make connections between contacts  73 . A wire  78  is connected between light-emitting device  75  and contacts  73 , as shown. Epoxy  76  and/or encapsulation epoxy  77  include phosphor material. For example, epoxy  76  is a YAG based phosphor, a variation of YAG based phosphors, a TAG based phosphor or a variation of TAG based phosphors. Other phosphor blends may also be used. For example, light-emitting device  75  is a deep UV light-emitting diode (LED) that emits light with a wavelength within a range of 160 nm to 290 nm.  
      The foregoing discussion discloses and describes merely exemplary methods and embodiments of the present invention. As will be understood by those familiar with the art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.