Effect and suppression of parasitic surface damage in neutron irradiated CMOS Monolithic Active Pixel Sensors

TL;DR

This paper investigates the effects of parasitic gamma radiation on neutron-irradiated CMOS MAPS sensors, revealing significant damage and proposing methods to identify and mitigate this parasitic ionizing radiation effect.

Contribution

It demonstrates that parasitic gamma radiation can cause notable damage in neutron-irradiated CMOS MAPS and introduces a procedure to recognize and suppress this effect.

Findings

Parasitic gamma radiation causes non-negligible damage in neutron-irradiated sensors.

Comparison shows gamma radiation damage is comparable to neutron damage under certain conditions.

Proposed procedure effectively identifies and suppresses parasitic ionizing radiation effects.

Abstract

CMOS Monolithic Active Pixel Sensors (MAPS) were chosen as sensor technology for the vertex detectors of STAR, CBM and the upgraded ALICE-ITS. They also constitute a valuable option for tracking devices at future e+e- colliders. Those applications require a substantial tolerance to both, ionizing and non-ionizing radiation. To allow for a focused optimization of the radiation tolerance, prototypes are tested by irradiating the devices either with purely ionizing radiation (e.g. soft X-rays) or the most pure sources of non-ionizing radiation available (e.g. reactor neutrons). In the second case, it is typically assumed that the impact of the parasitic $\gamma$-rays found in the neutron beams is negligible. We checked this assumption by irradiating MAPS with $\gamma$-rays and comparing the radiation damage generated with the one in neutron irradiated sensors. We conclude that the parasitic radiation doses may cause non-negligible radiation damage. Based on the results we propose a procedure to recognize and to suppress the effect of the related parasitic ionizing radiation damage.