New designs of CMS silicon pixel detectors for radiation hardness

New designs of silicon pixel detectors with n+/n/p+ and double-sided multiguard ring structures have been developed for more radiation-tolerant CMS forward pixel sensors. In a later design modification, guard rings on the n+ side are replaced with a single wide (640 μm) n+ implant, and the entire n+ side and the edge region of the p+ side are grounded. All designs were fabricated from both normal and oxygen-enriched silicon wafers, and radiation hardness effects for neutron (1 MeV equivalent) and proton (24 GeV) irradiation of these detectors were compared. Other electrical characteristics such as leakage current, potential distribution over guard rings and full depletion voltage were tested, using standard techniques of I–V, V–V, C–V and TCT before and after irradiation.