A new guard ring for radiation induced noise reduction in photodiodes implemented in 0.18 μm CMOS technology

Abstract

A new p-type guard ring by introduction of a thin p-type layer which encloses shallow trench isolation (STI) layer is utilized to reduce radiation induced noise in photodiodes implemented in 0.18 $\upmu$m standard complementary-metal-oxide-semiconductor (CMOS) technology. The guard ring efficiency is characterized according to a new radiation model developed for p–n photodiodes implemented in the same technology. The extracted model which is the oxide trapped charges and interface state values is verified using a simulation setup for two different structures. The optimized guard ring with the doping concentration of $10^{+19}$ atoms cm$^{-3}$ reduces the dark current of photodiodes at 1 Mrad dose of ionizing radiation from $6.97\,\times \,10^{-13}$ A (without the guard ring) to $1.29\,\times \,10^{-14}$ A for STI in contact with the active region structure and from $5.95\,\times \,10^{-13}$ A (without the guard ring) to $2\,\times \,10^{-14}$ A for STI surrounded p-well structure. The proposed guard ring can be used as a promising structure for ionizing radiation hardening of photodiodes.