Annealing studies on X-ray and neutron irradiated CMOS Monolithic Active Pixel Sensors

CMOS Monolithic Active Pixel Sensors (MAPS) integrate very small sensing elements with a pitch of 10-40 mu m together with analog and digital signal processing circuits into a monolithic chip, which may be thinned down to a thickness of similar to 50 mu m. These features make MAPS an interesting sensor for a broad range of vertex detectors in charged particle tracking (e.g. CBM, STAR, ILC). Intense R&D was performed in the last years in order to improve the radiation tolerance and hence the lifetime of the sensors toward the level required. One strategy to reach this improvement is reducing the number of metastable, radiation induced defects in the sensor material by thermal annealing. To test the feasibility of this approach, we studied systematically the effect of annealing on neutron and X-ray irradiated MAPS. The results of the studies are presented and the option to recover a strongly irradiated, MAPS based vertex detector by means of thermal treatment is discussed. (C) 2011 Elsevier B.V. All rights reserved.