A measurement of Lorentz angle and spatial resolution of radiation hard silicon pixel sensors

Silicon pixel sensors developed by the ATLAS collaboration to meet LHC requirements and to withstand hadronic irradiation to fluences of up to 10(15) n(eq)/cm(2) have been evaluated using a test beam facility at CERN providing a magnetic field. The Lorentz angle was measured and found to alter from 9.0degrees before irradiation. when the detectors operated at 150 V bias at B = 1.48 T, to 3.1degrees after irradiation and operating at 600 V bias at 1.01 T. In addition to the effect due to magnetic field variation, this change is explained by the variation of the electric field inside the detectors arising from the different bias conditions. The depletion depths of irradiated sensors at various bias voltages were also measured, At 600 V bias 280 mum thick sensors depleted to approximate to200 mum after irradiation at the design fluence of 1 x 10(15) 1 MeV n(eq)/cm(2) and were almost fully depleted at a fluence of 0.5 x 10(15) 1 MeV n(eq)/cm(2). The spatial resolution was measured for angles of incidence between 0degrees and 30degrees. The optimal value was found to be better than 5.3 mum before irradiation and 7.4 mum after irradiation. (C) 2002 Elsevier Science B.V. All rights reserved.