Speakers
Description
During the production of the new ATLAS Inner-Tracker (ITk) strip sensors for the forthcoming High-Luminosity Large Hadron Collider (HL-LHC) upgrade, the collaboration observed indications of low p-stop doping in a few sensor batches. Quality Control measurements of full-size sensors from these batches showed indications of sensor areas with low inter-strip isolation. Detailed studies of Quality Assurance test structures, such as MOS capacitors with p-stop or Punch-Through Protection structures, confirmed the deviation of parameters dependent on the p-stop doping, showing also inhomogeneity within some of the wafers. Although these sensor batches were identified and rejected, the performance of sensors with low p-stop doping after irradiation needs to be evaluated in detail to understand the possible consequences in HL-LHC working conditions.
This work presents a complete characterization of the inter-strip characteristics of full-size and miniature ATLAS ITk strip sensors irradiated with gammas and neutrons, covering a wide range of doses and fluences to disentangle the influence of the ionization and displacement damages on the defective p-stop isolation. The radiation levels ranged from one equivalent to the first days of the ITk detector in working conditions to the end of the 10-year lifetime of the experiment. The results are discussed in detail. The full-size sensors show a clear decrease of the inter-strip resistance for the sensors with low p-stop doping at all irradiation levels. Also, results from miniature sensors irradiated only with gamma doses show that miniature sensors with low p-stop doping reach values below the ATLAS specifications much earlier than standard miniature sensors with normal doping. In contrast, we observe that neutron irradiations increase the inter-strip resistance values for fluences above 4e14 neq/cm2, suggesting that displacement damage dominates over ionization impact for fluences accumulated after only a few months in working conditions, improving the inter-strip isolation and compensating for the deficiencies of low p-stop doping.
