Packaging of UV LED with a stacked silicon reflector for converged UV emission

Abstract

Focused ultraviolet (UV) emission is an ideal configuration to achieve in-situ curing. Conventional UV light-emitting diode (LED) packages, such as ceramic substrate packages, cannot achieve focused UV emission because they possess no reflector and lens, which are required to converge light. Plastic reflectors may be used, but common LED packaging plastics suffer from low UV reflectance and UV degradation issues. As an alternative to plastic reflectors, an aluminum coated silicon reflector stacked on another silicon substrate was proposed in the present study to converge UV emission. An optical model was developed to design the stacked silicon reflector. A ray tracing simulation was utilized to characterize the effect of the 2-layer stacked silicon reflector on the converged UV emission. With the addition of a stacked silicon reflector, the rays emitted from the UV LED chip are reflected towards the center axis of the package to increase the intensity. Compared with the emission from a UV LED package without a reflector, the maximum intensity of the UV LED package with a 2-layer stacked silicon reflector was 60% higher and the angular distribution of light was narrower. This indicated the UV energy was substantially converged. The stacked silicon reflector was fabricated by anisotropic wet etching and stacked by soldering. Further comparison with the profile of radiant intensity with various angles, the intensity at the center axis of the UV LED package with a 2-layer stacked silicon reflector was twice higher than that of the package without a reflector. In addition, the angular distribution of light of the sample with a 2-layer stacked silicon reflector was narrower than that of the sample without a reflector. It could be concluded that the stacked silicon reflector was able to converge UV emission. Furthermore, the ray tracing simulation was validated by experimental results. The optical model developed for this experiment could also be applied in other UV LED packaging designs.