Blue selective photodiodes for optical feedback in LED wafer level packages

Abstract

Recently applying an intelligent self-curing system to get a feedback from the LED light in order to control its intensity with driving current has attracted so much attention. This study presents a silicon stripe-shaped photodiode which is successfully designed and fabricated using a 2μm BiCMOS process. This process flow integrates simultaneously the photodiodes, the CMOS and BJT transistors all in just five masks. In this cheap and smart wafer level LED packaging, fabricated photodiodes demonstrated a very high selectivity to blue light. The maximum responsivity is at 480nm which is matched with the blue LED's illumination. The single-stripe photodiodes due to their higher rate of recombination caused by the dead layer formation at the surface showed lower responsivity compared to multi-stripe ones. The fabricated devices presented a two-fold increase in the responsivity and quantum efficiency compared to previously published sensors.