First annealing studies of irradiated silicon sensors with modified ATLAS pixel implantations

Planar silicon pixel sensors with modified n⁺-implantation shapes based on the IBL pixel sensor were designed in Dortmund. The sensors with a pixel size of 250 μm × 50 μm are produced in n⁺-in-n sensor technology. The charge collection efficiency should improve with electrical field strength maxima created by the different n⁺-implantation shapes. Therefore, higher particle detection efficiencies at lower bias voltages could be achieved. The modified pixel designs and the IBL standard design are placed on one sensor to test and compare the designs. The sensor can be read out with the FE-I4 readout chip. At the iWoRiD 2018, measurements of sensors irradiated with protons and neutrons respectively at different facilities were presented and showed incongruent results. Unintended annealing during irradiation was considered as an explanation for the observed differences in the hit detection efficiency for two neutron irradiated sensors. This hypothesis will be examined and confirmed in this work, presenting first annealing studies of sensors irradiated with neutrons in Ljubljana.