1 COMMON OPTICAL ELEMENT FOR AN ARRAY OF PHOSPHOR CONVERTED LIGHT EMITTING DEVICES
CROSS REFERENCE TO RELATED APPLICATION
The present application is a divisional application of and claims priority to U.S. patent application Ser. No. 12/099, 021, filed Apr. 7, 2008 abandoned, entitled “Array of Light Emitting Devices to Produce a White Light Source,” by Michael D. Camras et al., Which is a divisional application of and claims priority to U.S. patent application Ser. No. 10/987, 241, filed Nov. 12, 2004 U.S. Pat. No. 7,419,839, entitled “Bonding an Optical Element to a Light Emitting Device”, by Michael D. Camras et al, Which are all incorporated herein by reference.
The present invention relates generally to light emitting devices and, more particularly, to an array of light emitting devices to produce a White light source.
Adding or mixing a number of different color light emitting devices (LEDs) can be used to produce light With a broad spectrum. The spectrum produced, hoWever, consists of the peaks of the narroW band spectra produced by the individual LEDs. Consequently, the color rendering of such a light source is poor. White light sources With high color rendering, such as that produced by a halogen lamp, have a continuous or near continuous spectrum over the full visible light spectrum (400-700 nm).
Thus, a White light source With high color rendering that is produced using an array of LEDs is desired
In accordance With one embodiment of the present invention, a plurality of phosphor converted light emitting devices may be combined in an array to obtain light With a desired correlated color temperature (CCT). In one embodiment, the phosphor converted light emitting devices produce light With different CCTs. An array of the plurality of phosphor converted light emitting devices may be covered With an optical element that optionally can be filled With a material that assists in light extraction and mixing the light to produce light With the desired CCT. The optical element may be bonded to the phosphor converted light emitting devices. The optical element may be a dome mounted over the phosphor converted light emitting devices and filled With an encapsulant.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A illustrates a side vieW of an LED die mounted on a submount and an optical element that is to be bonded to the LED die.
FIG. 1B illustrates the optical element bonded to the LED die.
FIG. 2 illustrates an embodiment in Which multiple LED dice are mounted to a submount and a separate optical element is bonded to each LED die.
FIG. 3 illustrates an embodiment in Which multiple LED dice are mounted to a submount and a single optical element is bonded to the LED dice.
FIG. 4 is a floW chart of one implementation of producing such an LED device With Wavelength converting material covering the optical element.
FIG. 5 illustrates an embodiment in Which a layer of Wavelength converting material is disposed betWeen the bonding layer and the optical element.
FIG. 6 illustrates an embodiment in Which a layer of Wavelength converting material is deposited on the LED die.
FIG. 7 illustrates an array of LEDs, Which are mounted on a board.
FIG. 8 is a graph of the broad spectrum produced by a phosphor converted blue LED.
FIG. 9 is a CIE chromaticity diagram for the spectrum shoWn in FIG. 8.
FIG. 10 is a graph of the spectra produced by phosphor converted LEDs and colored LEDs, Which are combined to produce an approximately continuous spectrum.
FIG. 11 is a portion of a CIE chromaticity diagram that shoWs the variation in the CCT that may be produced by varying the brightness of the colored LEDs.
FIG. 12 is a portion of another CIE chromaticity diagram that illustrates variable CCT values for an array of 29 phosphor converted LEDs and 12 color LEDs.
FIG. 1A illustrates a side vieW of a transparent optical element 102 and a light emitting diode (LED) die 104 that is mounted on a submount 106. The optical element 102 is to be bonded to the LED die 104 in accordance With an embodiment of the present invention. FIG. 1B illustrates the optical element 102 bonded to the LED die 104.
The term “transparent” is used herein to indicate that the element so described, such as a “transparent optical element,” transmits light at the emission Wavelengths of the LED With less than about 50%, preferably less than about 10%, single pass loss due to absorption or scattering. The emission Wavelengths of the LED may lie in the infrared, visible, or ultraviolet regions of the electromagnetic spectrum. One of ordinary skill in the art Will recognize that the conditions “less than 50% single pass loss” and “less than 10% single pass loss” may be met by various combinations of transmission path length and absorption constant.
LED die 104 illustrated in FIGS. 1A and 1B includes a first semiconductor layer 108 of n-type conductivity (n-layer) and a second semiconductor layer 110 of p-type conductivity (p-layer). Semiconductor layers 108 and 110 are electrically coupled to an active region 112. Active region 112 is, for example, a p-n diode junction associated With the interface of layers 108 and 110. Alternatively, active region 112 includes one or more semiconductor layers that are doped n-type or p-type or are undoped. LED die 104 includes an n-contact 114 and a p-contact 116 that are electrically coupled to semiconductor layers 108 and 110, respectively. Contact 114 and contact 116 are disposed on the same side of LED die 104 in a “flip chip” arrangement. A transparent superstrate 118 coupled to the n layer 108 is formed from a material such as, for example, sapphire, SiC, GaN, GaP, diamond, cubic zirconia (ZrO2), aluminum oxynitride (AlON), AlN, spinel, ZnS, oxide of tellurium, oxide of lead, oxide of tungsten, polycrystalline alumina oxide (transparent alumina), and ZnO.
Active region 112 emits light upon application of a suitable voltage across contacts 114 and 116. In alternative implementations, the conductivity types of layers 108 and 110, together With respective contacts 114 and 116, are reversed. That is, layer 108 is a p-type layer, contact 114 is a p-contact, layer 110 is an n-type layer, and contact 116 is an n-contact.