Evidence of the lateral collection significance in small CMOS photodiodes

The lateral collection capacity of small CMOS photodiodes, scanned with a point source illumination, is studied. The mathematical solution of the physical equations is compared to experimental measurements in a standard UMC 90nm technology. They show close agreement and reveal that the lateral collection through the sidewalls of the depletion region becomes a significant component of the overall photocurrent. The same conclusion is achieved through device simulations under uniform illumination using ATLAS.