Reliability Testing of CRYO ASICs in a Cryogenic Environment and the Charge Collection System in nEXO's LXe TPC

For the nEXO project, we are developing ASICs for use in a time projection chamber (TPC) filled with liquid xenon enriched in Xe-136, a candidate for neutrinoless double beta decay. The TPC measures both charge and light signals from the liquid xenon to reconstruct events and suppress backgrounds, so that nEXO can look for evidence of neutrinoless double beta decay with sensitivity beyond 10²⁸ years. An important part of nEXO is the TPC’s charge collection plane, which must collect charge information from the liquid xenon at 165 Kelvin consistently over ten years. The connections from the charge collection plane carry low-level analog signals over short distances. To preserve signal integrity, these signals must be digitized soon after collection, requiring the ASICs to operate at liquid xenon temperature. The charge data from the charge collection plane is amplified, digitized, and serialized by nEXO’s CRYO ASIC, a System-On-Chip (SoC), and then forwarded to the data acquisition system. This work describes nEXO’s design for the charge collection plane of a LXe TPC to meet the strict energy resolution requirements and investigates the ASIC gain stability and in-situ calibration capability over time at liquid xenon temperature.