LEDs with remote phosphor layer and reflective substrate

Abstract

A light emitting device including a flip-chip light emitting diode (LED) die mounted on a substrate (12). The top surface of the substrate has a reflective layer. A hemispherical first transparent layer (36) is molded over the LED die. A low index layer (68) is then provided over the first transparent layer to provide TIR of the phosphorescence. A hemispherical phosphor layer (70) is then provided over the low index layer. A lens (72) is then molded over the phosphor layer. In combination with TIR at the interface of the high-index phosphor layer and the underlying low-index layer, the reflection achieved by the reflective substrate layer greatly improves the efficiency of the lamp. Other materials can be used. The low index layer can be an air gap (46) or a molded layer (68). In addition to the low index layer, a distributed Bragg reflector (76) can be sputtered on top of the first transparent layer.

Description

technical field [0001] The present invention relates to light emitting diodes (LEDs) having a phosphor coating to wavelength convert the LED emission, and more particularly to techniques for improving the efficiency of LED lamps using remote phosphors. Background technique [0002] To produce white light using a blue LED die, it is known to deposit YAG phosphor directly on top of the LED die, for example by spraying or spin coating the phosphor in an adhesive, electrophoresis, applying the phosphor in a reflective cup, or otherwise. or red and green phosphors. It is also known to attach a preform of phosphor (eg, sintered phosphor powder) on top of the LED die. Such phosphor layers are non-remote as they directly contact the surface of the semiconductor die. The blue light leaked through the phosphor combines with the phosphorescence to produce white light. Problems with using such non-remote phosphors include: 1) there is significant backscattering of blue light from the...

AI Technical Summary

Problems solved by technology

Problems with using such non-remote phosphors include: 1) there is significant backscattering of blue light from the phosphor layer, which is then partially absorbed by the LED, submount, and metal electrodes; and metal electrodes partially absorb a significant amount of light generated by the phosphor; 3) the photon density is extremely high for high power LEDs and saturates the phosphor; 4) the LED is very hot and the phosphor can react to heat to cause phosphorescence the darkening of the polymeric binder layer (e.g. silicone) in which the phosphor particles are embedded; and 5) the color varies with the perspective change

There is poor light extraction from the LED to the air gap and light is absorbed by the substrate

It is also quite difficult to manufacture such devices economically

Images