The present disclosure relates to a CMOS image sensor. The image sensor comprises a pixel region comprising a photodiode disposed within a substrate. A deep trench isolation (DTI) ring encloses the photodiode from top view and extends from a back-side to a first position within the substrate from cross-sectional view. A pair of shallow trench isolation (STI) structures is respectively disposed at an inner periphery and an outer periphery sandwiching the DTI ring from top view and extends from a front-side to a second position within the substrate from cross-sectional view. A pixel device is disposed at the front-side of the substrate directly overlying the DTI ring. The pixel device comprises a gate electrode disposed over the substrate and a pair of source/drain (S/D) regions disposed within the substrate and reaching on a top surface of the DTI ring.