Measuring Single Event Upset Cross Sections and Other Radiation Effects in Readout Electronics for the ATLAS Inner Tracker Upgrade

The ATLAS detector at the Large Hadron Collider (LHC) at CERN is in the process of upgrading its silicon charged-particle tracker as part of the Inner Tracker (ITk) upgrade, in parallel with the LHC’s own High-Luminosity upgrade (HL-LHC). With ten times the radiation dose expected at the HL-LHC as compared to LHC, the silicon technology used in the ITk must demonstrate an excellent radiation hardness to be performant over its lifetime. ATLAS Binary Chips (ABCs) are one such aspect of the ITk’s silicon technology, responsible for digitizing analog signals at the detector’s front-end. While generally resistant to total ionizing dose effects, ASICs like ABCs are susceptible to single event upsets (SEUs) whereby instances of radiation can flip a binary state, resulting in wrong outputs or even resets. We have measured the readout performance of ABCStars, the production version of ABCs, at testbeams using protons at TRIUMF and heavy ions at Louvain. The ASICs were irradiated up to doses of 4 Mrad. The total number of SEUs normalized to the total integrated fluence, the SEU cross section, was measured and found to be reduced when compared to earlier prototype ABCs, a result of protections implemented in the chip’s logic. Additionally, the measurements were used to quantify the increasing and then decreasing behaviour of the digital current pulled by the ASICs with accumulated ionizing dose. This confirms the validity of pre-irradiating ABCStars to guard against high current loads during runtime. Overall, these studies indicate excellent readiness of the ABCs for use in the ITk upgrade.