LAUSR

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 $$\upmu$$μm 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 $$10^{+19}$$10+19 atoms cm$$^{-3}$$-3 reduces the dark current of photodiodes at 1 Mrad dose of ionizing radiation from $$6.97\,\times \,10^{-13}$$6.97×10-13 A (without the guard ring) to $$1.29\,\times \,10^{-14}$$1.29×10-14 A for STI in contact with the active region structure and from $$5.95\,\times \,10^{-13}$$5.95×10-13 A (without the guard ring) to $$2\,\times \,10^{-14}$$2×10-14 A for STI surrounded p-well structure. The proposed guard ring can be used as a promising structure for ionizing radiation hardening of photodiodes.