Heavily Irradiated N-in-p Thin Planar Pixel Sensors with and without Active Edges

Abstract

We present the results of the characterization of silicon pixel modules employing n-in-p planar sensors with an active thickness of 150 $\mathrm{\mu}$m, produced at MPP/HLL, and 100-200 $\mathrm{\mu}$m thin active edge sensor devices, produced at VTT in Finland. These thin sensors are designed as candidates for the ATLAS pixel detector upgrade to be operated at the HL-LHC, as they ensure radiation hardness at high fluences. They are interconnected to the ATLAS FE-I3 and FE-I4 read-out chips. Moreover, the n-in-p technology only requires a single side processing and thereby it is a cost-effective alternative to the n-in-n pixel technology presently employed in the LHC experiments. High precision beam test measurements of the hit efficiency have been performed on these devices both at the CERN SpS and at DESY, Hamburg. We studied the behavior of these sensors at different bias voltages and different beam incident angles up to the maximum one expected for the new Insertable B-Layer of ATLAS and for HL-LHC detectors. Results obtained with 150 $\mathrm{\mu}$m thin sensors, assembled with the new ATLAS FE-I4 chip and irradiated up to a fluence of 4$\times$10$^{15}\mathrm{n}_{\mathrm{eq}}/\mathrm{cm}^2$, show that they are excellent candidates for larger radii of the silicon pixel tracker in the upgrade of the ATLAS detector at HL-LHC. In addition, the active edge technology of the VTT devices maximizes the active area of the sensor and reduces the material budget to suit the requirements for the innermost layers. The edge pixel performance of VTT modules has been investigated at beam test experiments and the analysis after irradiation up to a fluence of 5$\times$10$^{15}\mathrm{n}_{\mathrm{eq}}/\mathrm{cm}^2$ has been performed using radioactive sources in the laboratory.