Infrared and ultraviolet imaging with a CMOS sensor having layered photodiodes

Recently introduced CMOS sensors using three layers of photodiodes for color separation1 can also function well in the near ultraviolet and infrared bands. Ultraviolet sensitivity results from the close proximity of the top (blue) photodiode junctions to the surface of the silicon and the lack of any significant UV-absorbing materials above them. Infrared sensitivity extending nearly to the silicon band-gap cutoff results from depletion of the bottom (red) phodiodes into the substrate. Preliminary measurements indicate that the layered structure has high quantum efficiency over most of the 200-1100nm band covered by silicon photodiodes. Uniquely, these devices can be switched rapidly between narrowband monochrome imaging and full-color imaging in the visible band by the introduction of a visible pass filter. The response of the three photodiode layers is broad enough to permit stable false color encoding using two or three channels in conjunction with a redefinable 3 x 3 color transform matrix. Images have been acquired in the 300-400 nm UV band and for broad and narrow infrared bands out to 1064 nm. Thermal images of objects in the range of 600C have also been acquired demonstrating color-encoding of various UV, visible and IR bands and applications for particular encoding schemes.