Pitch dependence of the tolerance of CMOS monolithic active pixel sensors to non-ionizing radiation

CMOS monolithic active pixel sensors (MAPS) have demonstrated excellent performance as tracking detectors for charged particles. They provide an outstanding spatial resolution (a few μ m ), a detection efficiency of ≳ 99.9 % , very low material budget ( 0.05 % X 0 ) and good radiation tolerance ( ≳ 1 Mrad , ≳ 10 13 n eq / cm 2 ) (Deveaux et al. [1]). This makes them an interesting technology for various applications in heavy ion and particle physics. Their tolerance to bulk damage was recently improved by using high-resistivity ( ∼ 1 k Ω cm ) epitaxial layers as sensitive volume (Deveaux et al. [1], Dorokhov et al. [2]). diation tolerance of conventional MAPS is known to depend on the pixel pitch. This is as a higher pitch extends the distance, which signal electrons have to travel by thermal diffusion before being collected. Increased diffusion paths turn into a higher probability of loosing signal charge due to recombination. Provided that a similar effect exists in MAPS with high-resistivity epitaxial layer, it could be used to extend their radiation tolerance further. We addressed this question with MIMOSA-18AHR prototypes, which were provided by the IPHC Strasbourg and irradiated with reactor neutrons. We report about the results of this study and provide evidences that MAPS with 10 μ m pixel pitch tolerate doses of ≳ 3 × 10 14 n eq / cm 2 .