Optical design and characterization of micro-fabricated light reflector for 3D multi-chip LED module

LED module with multiple chips on silicon substrate becomes one of the mainstream light engine designs. Compared to conventional discrete LED package, which based on single die, module design with multi LED dies is necessary to fulfill the high luminous requirement for various lighting applications. Fabrication of the silicon based substrate can take the advantages of wafer level processes, which is a cost effective solution in massively parallel high throughput manufacturing and having the flexibility of scalability. Furthermore, the advances of silicon MEMS processing technologies open up the novel 3D module design consideration. The fabrication of 3D structure on silicon wafer can be realized by anisotropic etching based crystal direction and etchant selection. 3D cavities to embrace the LED dies, such as V-groove or trapezoidal basin, can be fabricated in by proper control of mask design and etch process. The fabricated cavities can then be coated with a reflective metal layer to become light reflectors. In this study, enhanced light extraction module design based on 3D reflector cavities is design and fabricated. The new design make used of the bulk micromachining process for tuning the reflector cup structure in order to effectively guiding the light emitted from the lateral surfaces of the LED dies. The optical performance related to the reflector geometries is examined by ray trace simulation. The light extraction can be improved by tuning the reflector placement and the depth of the reflector. The LED modules were fabricated and their optical performances were measured. The measured optical performance is presented and the design consideration is discussed.