Low temperature characteristics of SiPMs after very high neutron irradiation

The design of the CMS phase II upgrade for the HL-LHC uses SiPMs for the Barrel Timing Layer (BTL) and the Behind HCAL detector (BH or CEH). In both sub-detectors the SiPMs will see a 1 MeV equivalent dose of around n/cm. To lower the noise in the SiPMs the design is to keep the SiPMs at a low temperature of −30 C. Different samples from two manufactures of SiPMs were irradiated to a total dose of resp. 2 , 5 at the TRIGA reactor at the JSI in Slovenia. The noise in SiPMs is dominated by trap assisted tunneling which is a result of the high internal electric field in SiPMs. We therefore studied the noise behavior from ＋10 C to −40 C from standard high internal field and specially designed low field SiPMs from FBK-irst and Hamamatsu. After the initial characterization before annealing the noise decrease in SiPMs was also studied using accelerated annealing.