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Description
This work outlines the measurements done to evaluate the second SPACIROC generation in ionizing radiation environments, i.e., particle beams: ions, protons, and X-rays. The SPACIROCs are front-end ASICs designed for the readout requirements of photomultiplier technologies like: SiPMs, MaPMTs. Several radiation-induced effects were observed but they proved to be benign application-wise. The threshold LET for SEUs was measured and two cross-sections for different LETs are provided. At extremely high dose rates (~100 rad/s) and TID above 50 krad proton/X-ray induced TID effects were observed, however a room-temperature annealing process was determined to mitigate the harmful TID effects in 24 hours.
Summary (500 words)
The Spatial Photomultiplier Array Counting and Integrating Readout Chips (SPACIROC) are photodetector readout ASICs designed initially for the JEM-EUSO cosmic ray observatory. The second generation SPACIROC was a prototype version designed to evaluate the performance of several internal blocks before adopting the final design. The SPACIROC inherits the analog blocks from the third generation of Multi-Anode Readout Chip (MAROC3) ASICs, which are front-end ASICs proposed as backups for the LHCb-RICH MaPMT sensor readout. An irradiation campaign was organized to investigate the reliability of the SPACIROC2 in a radiation environment which emulates key characteristics of ISS environment or any LHC accelerator experiment. The SEE rates and the TID effects were measured using particle beams from various facilities: ions at LNL (Italy); 200 MeV protons at PSI (Switzerland); 35 MeV protons at Juelich Research Center (Germany); and 8-50 keV X-rays at University of Padova (Italy).
Two species of ions, 16O and 28Si -with LET values of (2.8 ± 0.3) MeVcm2/mg and (8.6 ± 0.8) MeVcm2/mg- were used to test the chips and to measure SEE rates for different beam-inclination angles and with various fluence values, up to (1.5 +/- 0.3) · 107 ions/cm2. Two values of SEU cross-section in configuration registers were measured: (〖"1.6" 〗"-1.4" ^"+4.18" ) · 10-6 cm2/device for a LET of (8.6 ± 0.8) MeVcm2/mg and (〖"0.5" 〗"-0.34" ^"+0.6" ) · 10-5 cm2/device for a LET of (11.2 ± 1.1) MeVcm2/mg. The SEU-threshold value was measured to be between (4.4 ± 0.4) MeV cm2/mg and (8.6 ± 0.8) MeVcm2/mg. No SEL was observed, and the few SEUs were mitigated by a reconfiguration of the device.
Using protons, and at very high and unrealistic dose rates, failures were observed in various build-in blocks, e.g., DACs. Increased leakage currents were observed due to TID, which were highly visible in the digital component of the ASIC. One sample was irradiated with 35 MeV protons in three runs of 50 krad (Si) each (total TID ~150 krad), which corresponds to a total fluence of (6.9 ± 0.33)·1011 protons/cm2. Three chips were irradiated with 200 MeV protons, each being subject to a TID of ~100 krad, and a fluence of about (2 ± 0.3) · 1012 protons/cm2. It was observed that the build-in DACs start to lose their linearity at a TID threshold between 80 and 100 krad. After 100 krad the DACs suffer complete failure. All previous TID effects were fully recovered through a rapid annealing process at room temperature within 24 hours to a few days, with no evidence of permanent effects or long-term effects even though one sample was irradiated with a cumulative TID of ~250 krad. No configuration SEUs were observed during irradiation with 35 MeV protons beam, though this measurement was for only one chip and smaller fluence, hence less conclusive. One chip was tested with X-Rays and a TID of ~117 krad and this measurement confirmed the TID effects observed in the proton-beam tests, separating these cumulative effects from the SEE class.
