The Al2O3 film contains a stable density of negative fixed charges. Typically, this density is in the region of 9E12/cm2. This creates an accumulation layer in the p-type substrate of the image sensor. This accumulation layer can effectively passivate the surface. It ensures that no photoelectric charges are trapped near the back surface and that thermally generated charges recombine. This reduces the dark current in backside illuminated image sensors. Other possible materials for the passivation layer include: Aluminiumfluoride (AlF3); Aluminiumoxynitride (AlON); Zirconiumoxide (ZrO2) under certain conditions; Calciumfluoride (CaF2). The Al2O3 film can serve as AR coating as well.
Samsung filed another application on RGB and depth sensor combination. The US20110102547 talks about RGB and IR color filter arrangement aimed to separate IR and RGB paths. Few different filter designs are proposed to achieve separation like this:
